ZnS:Cu nanocrystals were synthesized in polymeric networks. X-ray photoemission spectroscopy and atomic absorption data show that the Zn and Cu ion mass contents were about 8.2% and 0.12%, respectively. The particle size of ZnS:Cu nanocrystals was about 3.0nm, measured by UV-vis spectrum. Due to the quantum size effects, the band gap energy of ZnS nanocrystals was about 4.2eV. Compared with the photoluminescence of ZnS which peaks at 390nm, the photoemission of ZnS:Cu/polymer thin films was peaking at 415nm because of Cu acting as luminescent centers. The ZnS:Cu/polymer was also used to fabricate light-emitting diode (LED), as the emitting layer of LED, the blue light of electroluminescence was observed at room temperature, and its turn-on voltage was less than 4V.