PROBLEM TO BE SOLVED: To provide a slidability improving agent for injection molding, which comprises ultrahigh molecular weight polyethylene powder having fine particle size and consequently has excellent dispersibility in a thermoplastic resin being a matrix and which can allow a molding, particularly an injection molding, to be excellent in slidability such as friction characteristics and wear characteristics.SOLUTION: The slidability improving agent for injection molding comprises the ultrahigh molecular weight polyethylene powder having 15-40 dl/g intrinsic viscosity (&eegr;) and 1-10 μm average particle diameter.