This study was aimed at examining the therapeutic effects of marine collagen peptides (MCPs) from fish hydrolysate in Chinese patients with type 2 diabetes mellitus (T2DM). A total of 100 diabetic patients and 50 healthy controls were recruited. Diabetic patients were randomized into treatment and control groups. The patients in the treatment group received an additional 13 g of MCPs daily for 3 months. Their blood samples were collected before, and 1.5 and 3 months after, treatment to evaluate glucose and lipid metabolism. The levels of serum high-sensitivity C-reactive protein (hs-CRP), nitric oxide (NO), bradykinin, prostacyclin (PGI2), and adipokines were determined. Significantly reduced levels of fasting blood glucose, human glycated hemoglobin A1c (GHbA1c), fasting blood insulin, total triglycerides, total cholesterol, low-density lipoprotein, and free-fatty acids, but increased levels of insulin sensitivity index and HDL were observed in T2DM patients following treatment with MCPs for 1.5 and 3 months. The values of these measures were significantly lower or higher than those of patient controls (p < 0.01), respectively. Interestingly, significantly decreased levels of hs-CRP and NO, but increased levels of bradykinin, PGI2, and adiponectin were detected in MCP-treated T2DM patients (p < 0.01), as compared with their basal values or the levels in patient controls. MCP treatment improved glucose and lipid metabolism in diabetic patients.