For improvements of thermal stability and nonlinear optical (NLO) activity of chromophores, we newly synthesized a series of NLO chromophores incorporating aromatic benzoxazole unit as a π-conjugated bridge with various electron-withdrawing groups, such as nitrophenyl, nitrothiophene, nitrofuran, dicyanovinylphenyl, and nitrophenylethenyl group. Polymethylmethacrylate copolymers (PMBz) containing these benzoxazole chromophores were synthesized and their properties were investigated by thermogravimetry and ultraviolet-visible spectroscopy. The PMBz copolymers exhibited better thermal and ultraviolet stabilities than the corresponding copolymer with general stilbene chromophores (PMSt). Moreover, temporal stability of nonlinear optical coefficient (d 33) of PMBz copolymer increased in comparison with that of PMSt. The copolymer with benzoxazole-nitrothiophene chromophores had the largest d 33 value of 153 pm/V (at 1.064 mm) and nonresonant d 33 calculated by the two-level model was 21.3 pm/V.