Mono-dispersed and spherical cadmium sulfide (CdS) nanoparticles and cadmium sulfide/zinc sulfide (CdS/ZnS) nanoparticles, 4-5 nm in diameter, were synthesized in a heptane-AOT-water microemulsion system. The heat treatment of CdS and CdS/ZnS nanoparticles was annealed at 570 A degrees C under the air atmosphere. The heat-treated nanoparticles were of variable large sizes and had enhanced crystallinity. UV-Vis spectra of heat-treated CdS and CdS/ZnS nanoparticles revealed a flat shape similar to that of bulk CdS compounds. The difference between the PL emission bands of organic-coated nanoparticles and heat-treated nanoparticles was small. The PL emission energy of heat-treated nanoparticles was improved by about 2-3 times compared with that of organic-coated nanoparticles.