The UN cultural organisation has voted strongly in favour of membership for the Palestinians – a move opposed by Israel and the United States.
Of 173 countries voting, 107 were in favour, 14 opposed and 52 abstained.
Under US law, Washington can now withdraw funding to Unesco. This would deprive the agency of some $70m (£43.7m) – more than 20% of its budget.
The UN Security Council will vote next month on whether to grant the Palestinians full UN membership.