A refrigerator and an air purifier for a refrigerator are provided. The air purifier may include a case configured to be mounted on an upper surface of a cabinet of a refrigerator and in which inlet holes and an outlet hole are formed, a plurality of fan motor assemblies provided inside of the case to force a flow of air, a plurality of filter assemblies mounted in the case to partition a space between the inlet holes and the plurality of fan motor assemblies and purify suctioned air, a controller that controls driving of the plurality of fan motor assemblies, and a gas sensor connected to the controller to detect harmful gas in a kitchen space. The controller may control driving of the plurality of fan motor assemblies through detection of the harmful gas by the gas sensor.