The charity's founder, tycoon Li Ka-shing, is believed to own a stake of 0.4 per cent in Facebook through his charity the Li Ka-shing Foundation, which it acquired in 2007 for 60 million dollars, the South China Morning Post said.
With the company's value now estimated at 100 billion dollars, that stake is thought to be worth about 400 million.
The foundation - which makes grants to educational, health, cultural and community projects in Hong Kong - is believed to have acquired the shares after a Facebook investor introduced it to a director of the charity.
A charity representative refused to confirm the size of its investment in Facebook but said it was one of 25 technology companies in the foundation's portfolio, the Post said.
Li is one of Asia's richest men with an estimated fortune of 22 billion US dollars.
California-based Facebook filed for an initial public offering Wednesday.//DPA