Amplified spontaneous emission (ASE) characteristics of a green fluorescent dye (10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-[1] benzo- pyrano [6,7,8-ij]quinolizin-11-one) (C545T) encapsulated in a highly ordered three-dimensional (3D) inverted-opal titania (TiO(2)) photonic crystal (PC) microcavity were studied. Due to the utilization of a TiO(2) PC, the emission spectrum was greatly narrowed and the ASE threshold, gain, and loss were significantly improved. The threshold, gain, and loss reached 1.25 mJ pulse(-1) cm(-2), 34.69 cm(-1), and 16.9 cm(-1), respectively. The possible reason for the improvement in the ASE performance by the PC is attributed to the 3D photon localization by the microcavity effect of the PC.