Objective: To evaluate the effects of curcumin on regulating the proliferation, cell cycle distribution, apoptosis and relevant mechanisms in keratinocyte cell lines. Methods: The human immortalized human keratinocyte lines (HaCaT cells)were treated with different doses of curcumin. The effects of curcumin on cell viability were measured by MTT assay, and the cell cycle distribution and apoptosis determined by flow cytometry. The mRNA expression changes of proliferating cell nuclear antigen (PCNA), cyclin D1 and Bcl-XL were from real-time PCR analysis and the protein levels were detected by West blotting. Results: Data obtained in the study showed that curcumin could cause significantly inhibitory effect on proliferation in HaCaT cells in a time- and dose-dependent manner. Cell arrest at G1/S phase and significant apoptosis were observed after being treated with curcumin for 24 h. In association with these, the expression of PCNA, cyclin DI and Bcl-XL were decreased both at mRNA and protein levels for the same treatment. Conclusion: Curcumin can inhibit proliferation, induce cell arrest at G1/S phase and cause apoptosis in HaCaT cells. The decreased expression of PCNA, cyclin DI and Bcl-XL induced by curcumin contributes to the above effects in vitro.