PURPOSE: To obtain a low dynamic heat build-up polyurethane elastomer, by reacting a specified isocyanato group-terminated urethane prepolymer with a specified polyol.

CONSTITUTION: An isocyanato group-terminated urethane prepolymer obtained by reacting W1pts.wt. polyol having a molecular weight (MW1) of at least 500 and an (average) hydroxyl group functionality F1 of at least 2 with W2pts.wt. organic polyisocyanate having an (average) isocyanato group functionality F2 of at least is reacted with W3pts.wt. polyol having a molecular weight (MW3) of at most 5,000 and an (average) hydroxyl group functionality F3 of at least 2.2 to obtain a polyurethane elastomer wherein a nonreactive plasticizer is present in an amount corresponding to at least 4wt% of the total weight (W1+W2+W3), and the crosslinking density CD of the polyurethane elastomer as determined from the equation (wherein MW2 is the MW of the organic polyisocyanate) is 0.085 or more.