We examined the effects of polysaccharides extracted from Asterina pectinifera on the activities of quinone reductase (QR), glutathione S-transferase (GST), ornithine decarboxylase (ODC), cyclooxygenase (COX)-2 and glutathione (GSH) levels in HT-29 human colon adenocarcinoma cells. We found that the polysaccharides extract induced QR activity in a dose-dependent manner over a concentration range of $20-60;{mu}g/ml$ and increased GST activity as much as 1.4-fold over controls. GSH levels were increased 1.3- and 1.5-fold with the extract at 40 and $60;{mu}g/ml$, respectively. The activity and protein expression of ODC in 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced colon cancer cells was inhibited by the extract. The polysaccharides suppressed TPA-induced prostaglandin (PG) production. These data indicate that polysaccharides from A. pectinifera increase phase II detoxification enzyme activity and inhibit ODC and COX-2 activities in HT-29 human colon adenocarcinoma cells. Consequently, this effect may contribute to the protective effect of polysaccharides from A. pectinifera against colon cancer.