Terms of the deal were not disclosed, but Yahoo is said to be paying more than $100 million for the six-year-old start-up.
Associated Content boasts a network of 380,000 contributors – a concept similar to AOL’s Seed network and Demand Media.
For Yahoo, the deal gives it more content to offer advertisers.
"Combining our world-class editorial team with Associated Content’s makes this a game-changer," Yahoo CEO Carol Bartz said in a statement announcing the deal. "Together, we’ll create more content around what we know our users care about, and open up new and creative avenues for advertisers to engage with consumers across our network. These are important aspects of building engaging consumer experiences on Yahoo!, and one of the reasons why we’re one of the most visited destinations online."
Associated Content was founded by Luke Beatty in 2004.
In a blog post, Beatty said the deal "means a world of previously unimaginable growth opportunities."
According to comScore, the site averages about 16 million unique users per month.
Yahoo expects to complete the acquisition in the third quarter of 2010.
In a sign of the seismic shift occurring in the media world, though Associated Content lacks brand recognition, it sold for $95 million more than Business Week. In October, Bloomberg bought the well known magazine for $5 million. It was once valued at $1 billion.