Many epidemiological observational studies suggest that a high-fat diet (HFD) accelerates the risk of colorectal cancer (CRC). Inflammation can play a key role in the relationship between colon cancer and HFD. Although reported by several studies, controlled experimental studies have not explored this relationship. We established an HFD-fed colitis-associated colon cancer (CAC) mice model and evaluated the anti-tumorigenic effects of AG on HFD-propelled CAC along with its mechanism of action. Previously, we found that Aster glehni (AG) exerts chemopreventive effects on azoxymethane (AOM)/dextran sulfate sodium (DSS)-induced CAC in a mice model, and has anti-adipogenic effects in a HFD-induced obesity mice model. In the HFD-propelled CAC mice model, AG significantly reduced cancer-related death, prevented body weight loss, and alleviated splenic enlargement. Additionally, AG prevented colon shortening and reduced the number of colorectal polyps. Histological studies demonstrated the up-regulation of inflammation, hyperplasia, and neoplasia in HFD-propelled CAC mice, whereas AG suppressed colonic disease progression and tumorigenesis. Furthermore, AG significantly inhibited the signal transducer and activator of transcription 3 (STAT3) signaling pathway and attenuated the protein expression of the STAT3 target gene, which mediates transcription factor-dependent tumor cell proliferation. These results indicate that AG abrogates inflammation-induced tumor progression in HFD-propelled CAC mice by inhibiting STAT3 activation.