Numerous effective anticancer drugs have been developed from botanical sources, and there remains a significant untapped resource in herbal medicines. In this study, we evaluated the chemical composition of extracts from American ginseng after steaming, the antiproliferative effects of the ginsenosides in the extracts on SW-480 human colorectal cancer cells, and their apoptotic mechanisms. American ginseng roots were steamed at 120 degrees C for 2 or 4 h. Representative ginsenosides in the unsteamed and steamed extracts were determined using HPLC. The antiproliferative effects of the ginsenosides Rb1, Rg3 and Rh2 on SW-480 cells were determined by the MTS method. The effect of extract steamed for 4 h on apoptosis of SW-480 cell was assayed by flow cytometry after staining with annexin V/PI. The expression of 84 apoptotic-related genes, including TNF, mitochondria and p53 pathways, was determined using real-time quantitative PCR array analysis. The mitochondrial membrane potential (Deltapsim) was analyzed after staining with FC-1. Steaming of American ginseng increased Rg3 and Rh2 content and antiproliferative activity significantly. The quantitative PCR array data demonstrated that multiple genes in mitochondrial pathway are involved in American ginseng-induced apoptosis of SW-480 cells and the expression profiling was validated by the cellular functional assay. The mitochondrial pathway may play a key role in American ginseng-mediated cancer cell apoptosis.