PROBLEM TO BE SOLVED: To provide a plasticizer for a urethane resin which is low in volatility, a few in heating loss under a high-temperature environment, excellent in compatibility with a polyol which is a raw material of urethane resin, and reduces the viscosity of a solution blended with it; and to provide a urethane resin composition using the plasticizer, and a cured material thereof.SOLUTION: The plasticizer for urethane resin includes, as an essential component, an ester compound which is obtained by esterification of an aromatic polyvalent carboxylic acid (A) or its acid anhydride, and an aliphatic branched monoalcohol (B), wherein the value obtained by multiplying the valence number of the aromatic polyvalent carboxylic acid (A) by the C atom number of the aliphatic branched monoalcohol (B) is in the range of 33-100. There are provided an urethane resin composition using the plasticizer and a cured material thereof.