Why risk it ?

some of those pages have only links (about 40-50) in them with no content.

Define "content".

To me, a list of links is content.

In media production and publishing, content is information and experiences that may provide value for an end-user/audience in specific contexts.

And I have many pages with less content (atmost 2-3 lines). Is it valid to put google ads on those pages? about 900 pages in my site...

Risky.

As rule of thumb, you need enough content on the page for Google to be able to figure out what that page is about.

A links list certainly could be enough content, if the anchor text is meaningful (I'm assuming you don't, say, have 50 links, each of them consisting of a number 1, 2, 3, and so on). 2 or 3 lines, as Lame_Wolf said, would be risky. It's not enough. A full paragraph, with a header and a title--could be OK. I have some pages that provide very specific info. and on those I just put a 1-ad adblock, as I don't want the ads running down the page past the content. You might do that, on pages that meet a certain minimum.

Thank you all for your responses. A few follow up questions here..

1. The pages with lot of links in my site are pages with lists... like list of fruits, list of animals, list of cars etc.... those pages in turn have links to the actual pages like lists of animals contains links for all animals (tiger, lion etc.) and tiger link will lead the user to the page with information on tiger. So, my question is those lists pages have lots of links in them, with no text. Is it ok placing ads on those pages?

2. As far as pages with less content is concerend. Let's take the tiger page for example.. I have a h1 with Tiger in it.. and a para saying Tiger is an animal that lives in thick and dense forests. Is it ok placing google ads on that page?

Are these considered door way pages? Thanks again...

As far as pages with less content is concerend. Let's take the tiger page for example.. I have a h1 with Tiger in it.. and a para saying Tiger is an animal that lives in thick and dense forests. Is it ok placing google ads on that page?

A better question would be, "Is it worthwhile placing ads on that page?" I really doubt you'll get ads that your visitors will be all that interested in. Sometimes it's good not to put ads on every page...

Bear in mind that it is a *requirement* now for AdSense that you adhere to the Webmaster Guidelines for a good user experience.

Ask yourself truly - does this sound like a good user experience?

Ask yourself truly - does this sound like a good user experience?

I doubt it - if it's just a list of links. Unless they're ultra secret links others are after. OP said it was a directory. How many useless directories are there?

All MFA anyway.

A page of links is just that, a list of links. It's not content. This page here is content. A links page is merely one tiny step up from a blank page.

On my directory site I do have some pages with a list of links to specialist widget trade supplies, information or resources sites such as:

New widget machines
Used widget machines
Widget magazines
Widget forums
Widget portals etc etc

These type of pages are very popular in this directory since they are the only worldwide source for this information I have garnered over many years and I can assure you if one wanted to try and find this information simply by searching normally it would be almost impossible.

Depending upon the widget there will be between 20~200 links on a page.

All these pages rank #1 in Google and carry AdSense.

I'm not quite sure what the difference with your second example. It just seems to be the same as the first but with virtually nothing there except for a few words. What's the point of the page?

I purposely produce "index" pages with just a couple lines basically saying this is an index page to types of blue widgets. Then a list of different types of blue widgets each linking to the relevant page. The "relevant" page is not another list it's a real article. I have maybe twenty five of these index pages on a 1,000 page site.

Those index pages earn a nice income with a reasonably high CPM.

I got a site enticing to sign up & copy their contents of 1000 pages. If I sign up and download the content and copy it, would it be risky for indexing. May I use adsense in those contents . Or will be considered as duplicates & G will ban my account?
Or how could I save time and add content with some edits?
Appreciate feedback.

I got a site enticing to sign up & copy their contents of 1000 pages. If I sign up and download the content and copy it, would it be risky for indexing.

Possible, and most certainly for ranking.

May I use adsense in those contents . Or will be considered as duplicates & G will ban my account?

The only difference between someone scraping content and this, is that you have their permission, and if I were Google, I wouldn't allow it.

Or how could I save time and add content with some edits?

This sounds like you are in it for a quick buck. Forget it.
If you are serious about adsense, and serious about keeping your account, then write at what you are good at. Don't take, #*$!ize or pay for content that is already out there. Make it yours. Make it unique. Make it interesting so people will return.

Or will be considered as duplicates & G will ban my account?

Duplicate, you won't receive a ban however the pages won't rank either, well not very well normally, why would any search engine want duplication of pages?

Or how could I save time and add content with some edits?

Try Wikipedia...they've got plenty of scraped stuff from quality sites! :-)

At first, I thought "bad idea".

Then I thought about one of my review sites. There are about 7000 reviews on the site. Just about every page that isn't a review, is just a "list of links" for navigating to the reviews.

This site does not have adsense on it, but I would have no concerns about putting adsense on those navigation only pages. If your list of links, and the site in general, are useful, then you have little to worry about.

I would be a lot more concerned about those pages with little content. On my site, those 7000 reviews are the equivalent of magazine articles, all written specifically for the site. If someone from Google goes to your site, and follows links on those pages and keeps finding "content" pages with just a few lines, that's bad. They don't justify the ads on the low content pages OR the pages full of links.