Abstract: Yam polysaccharides and oat polysaccharides were both prepared using water extraction and alcohol precipitation methods.The intestinal microflora in a fecal extract from the health adults were used to ferment the two polysaccharides in vitro.The amount of four organic acids ( acetic, propionic, butyric and lactic acids) in the generated fermentation products were measured, and growth inhibition of these fermentation products on human colon cancer cells ( HCT-116 cells) were assessed.Yam polysaccharides and oat polysaccharides contained saccharide contents of 82.63% and 80.32%, respectively. Being fermented for 24 h, yam polysaccharides and oat polysaccharides generated acetic, propionic, butyric and lactic acids in levels of 23.28 and 25.14, 2.49 and 1.97, 11.04 and 7.99, 0.19 and 0.46 mmol/L, respectively. Being fermented for 48 h, yam polysaccharides and oat polysaccharides resulted in the levels of the four acids at 28.14 and 42.53, 6.48 and 2.45, 13.76 and9.64, 0.08 and 0.09 mmol/L, respectively. With the increase of fermentation time ( 24 ~ 28 h) , acetate, propionate and butyrate contents in fermentation products were enhanced clearly ( p < 0.05) , but lactate contents was also decreased markedly ( p <0.05) .Yam polysaccharides and oat polysaccharides showed lower growth inhibition ( less than 24.5%) on the HCT-116 cells.However, the obtained fermentation products exerted growth inhibition effect ( 46.2% ⁶9.1% and 44.6% ⁶7.3%, respectively) on the cells.And more, a fermentation time of 48 h conferred the fermentation products with higher growth inhibition while treatment of the cells for 48 h also led to higher growth inhibition.It is thus concluded that in vitro fermentation of the two polysaccharides by the intestinal microflora could bring enhanced anti-proliferation activities to the colon cancer cells.