Our previous studies confirmed that Coptis chinensis polysaccharide (CCPW) had a good antidiabetic activity and could improve insulin resistance. However, whether CCPW has a protective effect against the renal injury caused by diabetes has not been reported. In this study, the protective effect of CCPW against the renal injury of diabetic rats and its underlying mechanisms were investigated. The results showed that in CCPW-treated groups, the body mass of rats increased significantly, while the ratio of kidney weight to body weight decreased significantly; the 24-hour urine protein and the serum BUN and serum creatinine (Scr) levels decreased significantly, and pathological changes of the renal tissue were improved; superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) activities in the renal tissue were significantly higher, and malondialdehyde (MDA) contents in the renal tissue, and tumour necrosis factor-α (TNF-α), interleukin-6 (IL-6), and hypersensitive c-reactive protein (hs-CRP) levels in the serum were significantly lower; the expressions of phosphorylated tyrosine kinase 2 (p-JAK2) and activators of transcription 3 (p-STAT3) decreased significantly. The results indicate that CCPW should have a protective effect against the renal injury in diabetic rats, which may be associated with its inhibition on oxidative stress and inflammation.