Abstract: Unsaturated urethane having specified molecular structure shown by Formula (1) given below and vinyl monomers which are copolymerizable with such unsaturated urethane can form together polymerizable compositions which, as well as in-mold cured products therefrom, have improved characteristics such as compatibility between the constituents and water resistance: ##STR1## where X is a residual group obtained by removing the hydroxyl groups from a trihydric or tetrahydric polyol; R.sup.1 and R.sup.3 are each H or CH.sub.3 ; R.sup.2 is higher aliphatic hydrocarbon group with 5.about.21 carbon atoms; p and q are each 1 or 2; r is an integer 0.about.2 such that p+q+r=3 or 4 and p+r=2 or 3; and a is an integer 2.about.4.