The National Press and Publication Administration told state-run news agency Xinhua that game-playing would be only allowed between 8pm to 9pm.
It also instructed gaming companies to prevent children playing outside these times.
Earlier this month a state media outlet branded online games "spiritual opium".
Inspections of online gaming companies will also increase, to check that the time limits are being enforced the regulator said.
Earlier rules had limited children's online game-playing to 90 minutes per day, rising to three hours on holidays.
