Objective To observe the effects of curcumin on the proliferation and apoptosis of colon cancer cell line HCT-116 as well as on the changes in mitochondrial morphology and function，and to explore the potential mechanism. Methods Colon cancer cell line HCT-116 was cultured in vitro and treated with different concentrations of curcumin（5，10，20，and 30 μmol/L）. Cell count kit-8 was used to observe the changes in cell proliferation，and the optimal concentration was identified. Flow cytometry was used for determination of the changes in cell apoptosis. Mitochondrial membrane potential assay kit JC-1 was applied to determine the changes in intracellular mitochondrial membrane potential. Electron microscopy and Mito Tracker Deep Red staining were used for observing the changes in mitochondrial morphology and structure. The changes in cellular adenosine triphosphate（ATP） and reactive oxygen species（ROS） were assessed by the corresponding assay kits. The changes in the activities and protein levels of apoptosis-related caspase-3 and caspase-9 enzymes were measured by spectrophotometry and western blotting，respectively. Results After curcumin treatment，the proliferation of HCT-116 cells was significantly inhibited in a concentration-time dependent manner，and the half maximal inhibitory concentration was 13 μmol/L. Curcumin not only remarkably increased the proportion of cells in early apoptosis，but also significantly reduced the intracellular mitochondrial membrane potential level in a concentration dependent manner. The electron microscopy results showed that curcumin caused obvious mitochondrial swelling in cells，including crista swelling，disappearance，membrane rupture，and vacuoles. Mito Tracker Deep Red staining showed a significant decrease in mitochondria number and fragmentation appearance. The intracellular ATP production was significantly decreased. In addition，curcumin also increased the activities and protein expression of caspase-3 and caspase-9 enzymes in cells. Conclusion Curcumin inhibits the proliferation of colon cancer HCT-116 cells and promotes cell apoptosis. The mechanism is related to the aggravation of mitochondrial morphology and function damage by curcumin.