The green tea polyphenol (GTP) has been shown to possess cancer therapeutic effect through induction of apoptosis, while the underlying molecular mechanism of its anticancer effect is not well understood. PUMA (p53-upregulated modulator of apoptosis) plays an important role in the process of apoptosis induction in a variety of human tumor cells in both p53-dependent and -independent manners. However, whether or not PUMA is involved in the process of GTP-induced apoptosis in cancer cells has not been well reported. In the present study, we treated HT-29 (mutant p53) and LoVo (wild type p53) human colorectal cancer cells with different concentrations of GTP, which led to repression of cell proliferation and induction of apoptosis in both cell lines. Meanwhile, we also observed increased PUMA expression and decreased ERK (extracellular signal-regulated kinase) activity in both of GTP-treated tumor cell lines carrying different genotypes of p53. To determine the role of PUMA in GTP-induced apoptosis, we used stable RNA interference (RNAi) to suppress PUMA expression. As a result, apoptosis was abrogated in response to GTP-treatment. We also found that suppression of ERK activity by either RNAi or its specific inhibitor significantly enhanced GTP-induced PUMA expression. All these results indicate that PUMA plays a critical role in GTP-induced apoptosis pathway in human colorectal cancer cells and can be regulated partly by ERK inactivation. Demonstration of the molecular mechanism involved in the anti-cancer effect of GTP may be useful in the therapeutic target selection for p53 deficient colorectal cancer.