The well-crystallized ZnO nanoparticles were synthesized by a simple and facile soft chemical approach, and their induction of oxidative stress in Cloudman S91 melanoma cancer cells was studied. The ZnO nanoparticles were characterized for their morphology, structure, and optical properties. The ZnO nanoparticles with the average size of approximately 10 nm grew in high density, possessing wurtzite hexagonal phase. To study the induction of oxidative stress by ZnO nanoparticles in Cloudman S91 melanoma cancer cells, various doses of ZnO nanoparticles were treated with melanoma cancer cells for 24 h of incubation at 37 degrees C. The viability of the cells was analyzed with MTT method, whereas the morphology of the cells was observed via confocal laser scanning microscopy (CLSM), which revealed that when the time interval was increased, the number of cells decreased. The apoptosis-correlated, intracellular production of reactive oxygen species (ROS) was also measured with melanoma cancer cells with varying ZnO nanoparticle doses.