The news of the duo's meeting spread quickly, first through Chinese social networking sites and later through other news sites, sparking off speculation that the two companies may be planning to work together in the future.
The chief executive, who was named as this year's Person of the Year by Time Magazine, is on a holiday in China.
Zuckerberg and Baidu chief executive Robin Li toured Baidu's offices in Beijing and had lunch together, Baidu spokesman Kaiser Kuo told AFP.
"It makes sense - he is interested in the Chinese Internet, he's made that very plain. Obviously this is one of the big dark spots for Facebook, because it is blocked here in China," Kuo said about Zuckerberg's visit.
To an audience at Stanford University recently, Zuckerberg said that he was "spending a lot of time studying Chinese".
"How can you connect the whole world if you leave out a billion-six people?", he quipped.