The invention provides novel defoamers which are useful as defoamers for top coat paints for motor vehicles. When the defoamers are incorporated with paints which do not use melamine resins as the curing agent, they can impart defoaming property to the paints without inviting turbidity in the painted films caused by infiltration of water. Hence the defoamers are particularly useful when used for baking finish type clear top coat paints for motor vehicles. The defoamer is characterized by comprising a copolymer of 2-50% by weight of (A) a polymerizable monomer capable of forming a copolymer having isocyanate groups which can react with a binder resin in thermosetting type paint or (b) a polymerizable monomer capable of forming a copolymer having the groups which produce isocyanate groups reactable with a binder resin in thermosetting type paint during the baking step of the same paint, and 98-50% by weight of (C) a monomer or polymer conventionally used for defoamers.