Recent research has focused on zinc oxide nanoparticles (ZnO NPs) in culture and in vivo cell lines due to their cytotoxic potential. In addition, ZnO has garnered considerable interest in cancer therapy. Our objective was to assess the cytotoxicity of ZnO NPs on cell lines from the ovary, prostate, and bone (SK-OV-3, PC3, and Saos-2). ZnO nanoparticles were used to culture SK-OV-3, PC3, and Saos-2 cancer cells at concentrations of 0, 20, 40, 80, 160, and 320 ppm. Cancer cells were subsequently incubated for 24 and 48 h. Using the MTT assay, the apoptosis and cytotoxicity of cells were quantified. ZnO NPs of both diameters exhibited cytotoxic properties. Regardless of the lowest concentration, the extent of the cytotoxic effect on apoptosis is 32.55 nm. A rise in ZnO NP concentration was associated with an increase in apoptosis and a decrease in viability. The findings of this study suggest that the examined cancer types exhibited cytotoxic effects upon exposure to ZnO NPs, as compared to the control group that was not exposed. Furthermore, the maximum cytotoxic effects were observed at higher concentrations. It seems that the observed increase in cytotoxicity may not be significantly altered.