Yahoo has reached a deal to run the display and video advertising which appears on the website of US cable television giant Comcast.
Yahoo has made a series of deals as it competes with Google
The deal is the latest in a series by Yahoo, which is expanding from its core search and pay-per-click advertising to compete better with Google.
Other recent moves have included deals with Viacom and NBC Universal.
Yahoo has also spent $680m (£340m) buying out the remaining 80% of online advertising exchange Right Media.
Yahoo bought an initial 20% of Right Media in October for $40m.
Right Media is an online exchange that tries to create a more transparent advertising market by making it easier for web publishers to show what they have to offer to online advertisers.