Colorectal cancer is the third most common malignant tumor with high morbidity and mortality. To evaluate the antitumor effect of genkwanin on colorectal cancer enhanced by western high-fat diet, we investigated the activity of genkwanin on HT-29 and SW-480 human colorectal cancer lines in vitro and on the APCMin/+ mice in vivo. In a cell culture system, six different inflammatory cytokines obviously stimulated two cancer cells growth in a concentration-dependent manner, while genkwanin significantly inhibited HT-29 and SW-480 human colorectal cancer cells proliferation and inflammatory cytokine IL-8 secretion. In the APCMin/+ mice, the body weights, spleen and thymus indexes and immunity cytokine secretions were significantly improved after oral administration 12.5 and 25 mg/kg/day of genkwanin. Besides, the tumor multiplicity changes and inflammatory cytokine levels were markedly reduced in two genkwanin-treated groups. The dysplastic adenomatous changes were also obviously ameliorated in gut histopathology. Taken together, our results indicated that genkwanin had a better antitumor activity partly via enhancing host immunity and decreasing the inflammatory cytokine levels. Genkwanin may be an effective chemotherapeutic agent for the treatment of colorectal cancer.