We synthesized two new diol monomers with benzoxazole-based nonlinear optical (NLO) chromophores, one of which has an additional hydroxyl group as a crosslinkable moiety and the other has a nitrothiophene group as an electron withdrawing unit. The diol monomers were polymerized with 4,4＇-methylenebis(phenyl isocyanate) to give NLO polyurethanes, respectively. Linear polyurethane with hydroxyl groups could be crosslinked between side chain chromophores themselves after poling using an additional crosslinking agent such as teramethyl-1,3-xylylene diisocyanate. Temporal stability of electro-optic coefficient of a crosslinked polyurethane was improved compared with that of a linear polyurethane. The second harmonic generation coefficient of linear polyurethane with benzoxazole-thiophene chromophores was 94 pm V-1 (1.064 mu m) and nonresonant d(33) value was 17.1 pm V-1 calculated by two-level model equation.