Cinnamon (肉桂 ròu guì) has in vitro insulin potentiating activity, and proanthocyanidins from cinnamon prevent in vitro formation of advanced glycation end products. Some human studies were equivocal, but several have shown beneficial effects of cinnamon supplementation on circulating glucose, lipids, and/or insulin. This placebo-controlled double-blind trial tested the effects of a dried water extract of cinnamon (Cinnamomum cassia) on circulating glucose, lipids, insulin, and insulin resistance. Men and women from Beijing and Dalian, China, were invited to participate if they had fasting serum glucose >6.1 mmol/L or 2-h glucose >7.8 mmol/L. Participants, (173 were enrolled and 137 completed the study) were randomly assigned to receive either a spray-dried, water extract of cinnamon (CinSulin®), 250 mg/capsule, or a placebo, twice a day for two months. Mean ± SEM age of participants was 61.3 ± 0.8 years, BMI was 25.3 ± 0.3 and M/F ratio was 65/72. After 2 mo, fasting glucose decreased (p < 0.001) in the cinnamon extract-supplemented group (8.85 ± 0.36 to 8.19 ± 0.29 mmol/L) compared with the placebo group (8.57 ± 0.32 to 8.44 ± 0.34 mmol/L, p = 0.45). Glucose 2 h after a 75 g carbohydrate load, fasting insulin, and HOMA-IR also decreased with cinnamon extract compared with placebo. Total and LDL-cholesterol decreased with cinnamon extract and HDL-cholesterol decreased in both the cinnamon-extract and placebo groups. In conclusion, supplementation with 500 mg of water-extract of cinnamon for two months reduced fasting insulin, glucose, total cholesterol, and LDL cholesterol and enhanced insulin sensitivity of subjects with elevated blood glucose.