The moratorium covers the 500,000 people living in the 32-square mile area of South Los Angeles, which is predominantly Hispanic and African-American.
Designed to encourage healthier eating habits, the move is believed to be the first time fast-food outlets have been restricted from opening on health grounds.
A spokeswoman for the law's sponsor, Los Angeles City councillor Jan Perry, said the law was approved 12-0 during a hearing on Tuesday that was interrupted by a 5.
4 magnitude earthquake that hit the region.
Under California law, fast-food restaurants are defined as establishments which have a limited menu, sell items prepared in advance or heated quickly, have no table orders and serve food in disposable packaging.
Perry described the ordinance's approval as a "victory for the people of South Los Angeles."
"We need to attract sit-down restaurants, full service grocery stores and healthy good alternatives and we need to do in an aggressive manner," Perry said in a statement.