Mr Lewis, who is now one of the funds' largest shareholders, filed his stock purchases with the US Securities and Exchange Commission (SEC).
According to the SEC filing, his stock is now higher than that of any other shareholder - Putnam Investment Management was Bear's largest shareholder before him.
Shares in the US investment bank are down by about 35 per cent this year, after the collapse of two hedge funds in the wake of the sub-prime mortgage crisis.
Mr Lewis is said to be worth $2.5 billion and Forbes ranked him as number 369 in their billionaire list.
Tavistock Group, the investment vehicle run by Mr Lewis holds interests in about 170 companies in 15 countries around the globe.
Tottenham Hotspur football club and various golf developments in Florida are among his investments.
Shares in Bear Stearns were up by 0.6 per cent and trading at Â£106.03 on the New York Stock Exchange.