The commercial nanoparticles ZnO with - P63mc hexagonalstructure, particle size of hundreds of nanometer and band gap energy about of3.26 eV have been used on photocatalyst for methylene blue. The results showedthat as increasing irradiated time from 30 minutes to 120 minutes by 365 nmradiation of Narva LT 18W ultra - violet lamp, the color of methylene-blue andZnO mixture were depleted gradually, in which the absorptance andphotoluminescence intensity were also decreased. The cause of these phenomenahas been studied and explained. The role of ZnO nanopowder photocatalyst forVan Phuc dye wastewater (Ha Dong district, Hanoi city) has been tested by the first step