A series of novel asymmetrical mono-carbonyl analogs of curcumin (AMACs) were synthesized and evaluated for cytotoxic activity using BSLT and MTT assay against Vero, HeLa, and MCF7 cell lines. The structures of the synthesized compounds were confirmed by FTIR, 1H-NMR, 13C-NMR, and mass spectral data. The results of the cytotoxicity evaluation showed that the synthesized compounds exhibited moderate to very high toxic activity in BSLT (LC50 value 29.80–1704.23 µM); most of the compound exhibited cytotoxic activity against HeLa cell lines, which is comparable to the activity of cisplatin (IC50 value 40.65–95.55 µM), and most of the compound tested against MCF7 cell lines exhibited moderate to very high cytotoxic activity (IC50 value 7.86–35.88 µM). However, the selectivity index (SI) of the compounds was low (<1–1.96). Among the synthesized compounds, compound 1b was the most cytotoxic and selective against MCF7 cell lines. It could be considered for further development to obtain the more active and selective chemotherapeutic agents against breast cancer.