The　samples　of　nano-size　ZnO　were　prepared　by　precipitation,　hydrolysis,　sol-gel　method　and　characterized　by　X-ray　diffraction,　Uv-Vis　diffuse　reflection　spectrum,　and　time　resolved　luminescent　spectrum.　The　results　showed　that　the　crystallite　dimensions　of　all　ZnO　samples　were　coarsening　with　increasing　annealing　temperature　and　the　grain　sizes　prepared　by　sol-gel　method　were　obviously　smaller　than　the　others　prepared　by　precipitation　and　hydrolysis　method.　Under　excitation　of　monochromatic　light　of　wavelength　300nm,　a　strong　and　broad　photoluminescence　(PL)　emissions　were　observed　in　the　wavelength　range　of　420　similar　to　780nm.　As　the　grain　size　decreased,　the　PL　peak　positions　moved　to　shorter　wavelengths.　And　as　the　annealing　temperature　increased,　the　peak　intensity　decreased.　The　photoluminescence　decay　profile　of　ZnO　was　well　described　by　three　decay　components　of　46ns,　330ns　and　1630ns.