A well-defined n=1 heavy-hole exeiton absorption peak from a loealized state and n=2 heavy-hole exeiton emission peak was observed in a ZnCdSe/ZnSe single quantum well structures at 77 K. The localized state was formed by fluctuation of well-barrier interfaces. Stimulated emission was observed from the localized state. The gain originate from exeiton phase space fill of these state. An optical excitation threshold around 116 kW/cm2 was measured. The gain switching was observed. These results were obtained from photoluminescence under oaring excitation power, and luminescence decay experiments.