Context:Argemone mexicanaLinn. (Papaveraceae) has been used as traditional medicine in India and Taiwan for the treatment of skin diseases, inflammations, bilious, fever, etc. Some alkaloids ofA. mexicanahave been screened for their cytotoxicity on different cancer cell lines. Objective: The study investigates potential cytotoxic effects of alkaloids isolated from aerial part ofA. mexicanaon SW480 human colon cancer cell line. Materials and methods: Six alkaloids, 13-oxoprotopine, protomexicine, 8-methoxydihydrosanguinarine, dehydrocorydalmine, jatrorrhizine, and 8-oxyberberine were isolated from the methanol extract ofA. mexicana. Cytotoxicity of these alkaloids was studied on SW480 human colon cancer cell line at 1, 25, 50, 75, 100, 125, 150, and 200 µg/mL for 24 and 48 h. Cells were seeded in a 96-well micro-plate at a concentration of 2 × 104cells per well and MTS assay was performed to assess cytotoxicity in terms of cell viability. Results: At 200 µg/mL, protomexicine and 13-oxoprotopine showed mild cytotoxicity (∼24–28%) whereas dehydrocorydalmine exhibited moderate cytotoxicity (∼48%). 8-Oxyberberine was mildly cytotoxic (∼27%) at 24 h but was more potent (∼76%) at 48 h. Jatrorrhizine and 8-methoxydihydrosanguinarine were most potent (∼95–100%) in inhibiting the human colon cancer cell proliferation showing complete reduction in cell viability. Discussion and conclusion: This is the first study on the effect of these alkaloids on SW480 human colon cancer cell line. This study indicates that some alkaloids ofA. mexicanastrongly inhibit the cell proliferation in human colon cancer cells, and it might be a basis for future development of a potent chemotherapeutic drug. [ABSTRACT FROM AUTHOR]