Quantum dots (QDs) of direct band gap semiconductor cadmium sulfide (CdS) were synthesized using aqueous CdCl2 and Na2S by microemulsion method at 303 K. The cationic surfactant cetylpyridinium chloride (CPC) and cosurfactant 1-pentanol were used in water in heptane emulsion to form reverse micelles. The broad X-ray diffraction pattern and clear lattice fringes in the high-resolution transmission electron microscope (HRTEM) images indicate cubic phase of the CdS nanocrystals. The zero dimensional nature of the synthesized particles was observed in the field emission scanning electron microscope (FESEM) image. The average size of the obtained nanoparticles was 4.8 nm. Optical properties revealed that the change of band gap energy from its bulk value of 2.4 to 2.8 eV due to the typical quantum size effects. Blue shift was observed in the photoluminescence (PL) spectrum.