Icahn, a billionaire hedge-fund manager who threatened to oust Yahoo's board this summer after it rejected a deal with Microsoft Inc., snapped up about $67 million worth of shares over three days this week, according to a filing with the Securities and Exchange Commission.
Icahn bought 6.8 million shares for an average of $9.92 each in three batches from Monday through Wednesday, bringing his total stake to 75.6 million, or nearly 5.5 percent of the company, according to the filing made Wednesday.
In his original $1.5 billion investment in Yahoo, Icahn paid an average of about $25 dollars per share.
Yahoo's stock rose 93 cents, or 8.8 percent, to $11.51 Friday.
Yahoo is looking for a new chief executive after co-founder Jerry Yang said earlier this month that he will step down as soon as the board finds a successor.
Icahn has been among the loudest voices arguing for a new direction at Yahoo. He threatened to nominate a new slate of directors after the Sunnyvale, Calif., company rejected a $47.5 billion takeover offer from Microsoft this summer. Yahoo gave him a seat on its board and two other slots for members of his choosing.
Microsoft head Steven A. Ballmer, after making two unsuccessful bids, now says he isn't interested in buying the whole company, though he has expressed interest in the search business.