A new third-order nonlinear optical polyimide with aluminum phthalocyanine unit as a side-chain (APSPI) has been developed. The poly(hydroxyimide) (PHI) was prepared by the ring-opening polyaddition of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride with 4,4'-diamino-4"-hydroxytriphenylmethane, followed by thermal imidization. The resulting PM had number-and weight-average molecular weights (M-n, M-w) of 34,000 and 64,000, respectively. The introduction of aluminum phthalocyanine, unit (AlPc) to PHI was carried out by the reaction of PHI with chloroaluminum phthalocyanine in the presence of silver triflate. The third-order nonlinear susceptibility chi(3) of APSPI film with approximately 60 mol% content of AlPc at 1064 nm wavelength was 5.3 X 10(-9) esu. This was measured using the closed Z-scan technique.