MTT assay and flow cytometry analysis were used to examine the anti-liver (HepG2) and anti-breast cancer (MCF-7) activities of twelve compounds derived from 2-thioxo-4-imidazolidine. The compounds 5a–h and 7g demonstrated significant anticancer activity against breast cancer cells, while the compounds 5a, 5b, and 5d–h demonstrated significant anticancer activity against liver cancer cells, with varying IC50 values as compared to Cisplatin as the positive control. Among these compounds, we chose 5a, 5d, and 5h to detect cell-cycle phases and late apoptosis. Compound 5a arrested MCF-7 cells in the S phase, while compound 5d arrested cells in the G1 phase. Compound 5a arrested S phase HepG2 cells, compound 5d arrested S phase cells, and compound 5h arrested G2 phase HepG2 cells. Compound 5a had a higher ratio of late apoptosis than compounds 5d and 5h on both cancer cells. Finally, further research will be conducted to develop these compounds as new anti-breast and anti-liver agents.