Purpose: To study the mechanism of chemoprevention of colorectal cancer by aspirin. Methods: Different concentrations of aspirin have been used in the culture of colonic cell-Caco-2, its proliferation and apoptosis was observed during the culture and the expression of Fas/FasL mRNA was assayed by RT-PCR. Results: Major portion of cells died in the culture medium that was added high concentration of aspirin, but the lower concentration promoted apoptosis. The Fas mRNA was expressed in cells added with 25 mmol/L aspirin, but not in that of 1640. The FasL mRNA expressed in 25mmol/L aspirin was lower than in 1640. Conclusions: The lower concentration of aspirin can promote apoptosis of coloniccell, the mechanism has correlation with induction of the expression of Fas, and down-regulation of the expression of FasL.