South Korea's government says the sanctions on 20 North Korean groups and 12 individuals took effect from today.
Seoul is among the first to respond to North Korea's November 29 missile launch with fresh sanctions. The government says it hopes its move will prompt the international community to do likewise.
US President Donald Trump's UN ambassador has been urging the world to cut trade and diplomatic ties with Pyongyang.
Separately, South Korea, the United States and Japan started their two-day missile tracking drills today.