A process for producing a thermoplastic polymer powder that is made by subjecting an acrylic triblock copolymer (B)(A)(B) to an underwater cutting process to obtain a thermoplastic polymer powder, wherein block (A) has structural units originating from an acrylic ester; and block (B) has structural units originating from a methacrylic ester, this thermoplastic polymer powder is suitable for use as molding, skin material, and the like which are excellent in weatherability, flexibility, mechanical strength, low-temperature properties, adhesion to polar resins, rubber elasticity, safety, etc.