Two‐photon pumped frequency upconversion cavity lasing at ∼610 nm is accomplished in a dye‐doped polymer fiber system, pumped with ∼12 ns and 1.06 μm IR laser pulses. The dopant is a novel dye, trans‐4‐[p‐(N‐hydroxyethyl‐N‐methylamino)styryl]‐N‐methylpyridinium iodide, abbreviated as ASPI, which possesses a greater two‐photon absorption cross section and stronger upconversion fluorescence emission compared to common commercial dyes (such as rhodamine 6G). Using a Q‐switched Nd:YAG pulse laser as the pump source, cavity lasing could be achieved in a 3‐cm‐long ASPI‐doped poly(2‐hydroxyethyl methacrylate) solid fiber of 100 μm diameter. The experimental results of spectral, temporal, spatial, and input–output characteristics of the cavity lasing are presented. The slope efficiency of upconversion lasing was 0.9%. © 1996 American Institute of Physics.