Chronic inflammation raises the risk of the development of colorectal cancer (CRC). Green tea catechins (GTCs), which possess anti-inflammatory properties, are known to be anti-carcinogenic in a variety of organ sites, including the colorectum. This study investigated whether (-)-epigallocatechin gallate (EGCG), a candidate chemopreventive agent and major biologically-active component of green tea, and Polyphenon E (Poly E), a mixture of GTCs, suppress inflammation-related colon carcinogenesis induced by azoxymethane (AOM) and dextran sodium sulfate (DSS). Male ICR mice aged 5 weeks were given a single intraperitoneal injection of AOM (10 mg/kg body weight), followed by 2% (w/v) DSS in drinking water for 7 days to induce colitis-related colonic tumors. They also received drinking water containing EGCG (0.01 or 0.1%) or Poly E (0.01 or 0.1%) up to week 17. At week 17, treatment with EGCG or Poly E had significantly suppressed the multiplicity and volume of colonic neoplasms as compared to the AOM/DSS group, and had resulted in a lesser degree of malignancy. In addition, treatment with EGCG or Poly E decreased the protein and mRNA expression levels of Cyclooxygenase (COX)-2 and the mRNA expression of inflammatory cytokines (TNF-α, IFN-γ, IL-6, IL-12 and IL-18) in the colonic mucosa. Our findings provide evidence that tea catechins are beneficial to the suppression of cancer development in the inflamed colon.