The move comes less than a month after it snapped up 92.8 per cent of French holiday resorts group Club Med.
A statement to the Hong Kong stock exchange, where Fosun is listed, said the company had bought the stake, worth 91.8 million pounds (USD 140 million), at 125.59 pence per share.
"The Group intends to purchase further Thomas Cook shares on the open market at the appropriate time," the statement said, adding that the company was seeking to take its stake to around 10 per cent.
Fosun shares closed slightly up at HK$12.78 (USD 1.65), a rise of 0.18 per cent.
Privately-owned Fosun, which is based in Shanghai and controlled by Chinese billionaire Guo Guangchang, is a diversified conglomerate with interests ranging from media to pharmaceuticals and mining.
The statement from the company said that the move would "capitalise on the increasing demand for international leisure travel".
"The investment in Thomas Cook complements other recent investments of the Group in the sector, providing opportunities for further value creation," it said.
