A study of the photoluminescence (PL) spectra in ZnSe-ZnS strained layer superlattices (SLSs) with various ZnSe well-layer thicknesses was investigated by PL measurements. An intense excitonic-emission line, and no emissions due to deep levels, were observed. As the ZnSe well-layer thickness is decreased, the peak of the line largely shifted towards the higher-energy side. This behavior may be related to the quantum size effect. In the temperature dependence of PL intensity, this is the thermal quenching process, which may be related to the thermal release of excitons in the quantum well, As the thickness of the ZnSe well-layer is decreased, the activation energy increased.