We prepare a polyvinyl alcohol film containing undoped and Mn2+-doped CdS nanocrystals by a chemical method, and investigate the photoluminescence properties. The luminescence of Mn2+ of this sample shows long decay times of about 1.1 and 0.2 ms. unlike the previous report on ZnS:Mn2+ nanocrystals. Under the interband excitation, the temperature quenching of the Mn2+ luminescence is found to be remarkably weak in comparison with the bulk crystals of CdS:Mn2+. Probable causes of this difference are discussed in terms of the electron-hole pair (or exciton)-phonon interaction and the thermally induced dissociation of the electron-hole pair. Further, we measure site-selective luminescence spectra and discuss the origin of the green luminescence of the undoped CdS nanocrystals.