Alwaleed, whom Forbes magazine considered the wealthiest man in the oil-rich kingdom, made the announcement at a press conference in Riyadh.
He said he was pledging his entire fortune with special focus on humanitarian concerns.
The prince, who has two children, did not give a timetable for his donation.
Bill Gates has given 28 billion dollars from his fortune to charity, while Warren Buffet has donated 23 billion, according to Forbes.
The two Americans set up the Giving Pledge in 2010, an initiative aimed at convincing the world’s wealthiest people to give most of their money to philanthropy.