The effects of polysaccharide extracted from Lycium barbarum (LBP) on blood glucose, oxidative stress and DNA damage in rats with non-insulin dependent diabetes mellitus (NIDDM) were studied. The results show that LBP treatment (10 mg/kg.d) for 4 weeks led to decreased levels of blood glucose, malondialdehyde (MDA) and nitric oxide (NO) in serum of fasting rats; and to increased serum level of superoxidedismutase (SOD). Furthermore, LBP could reduce cellular DNA damage in peripheral lymphocytes of NIDDM rats. The DNA damage was determined by using the single cell gel (comet) assay with alkaline electrophoresis and was quantified by measuring tail length and tail moment. These results suggest that LBP can control blood glucose and modulate the metabolism of glucose, leading to significant improvement of oxidative stress markers (SOD, MDA) in rats with NIDDM. And that, LBP decreases DNA damage possibly via a decrease in oxidative stress levels. In conclusion, LBP as a dietary supplement may prevent the development of complications or even tendency to carcinogenesis in NIDDM rats.