Google is also believed to be interested in taking a stake in the popular site.
The Wall Street Journal reports that Microsoft wants around 5% of Facebook, and is willing to pay up to £250m for the stake.
Microsoft and Google will not comment on their reported interest in Facebook, but Redmond already has a close marketing and advertising relationship with the site.
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Facebook has more than 40 million users worldwide. Bebo is the most popular social networking site in the UK.