Background: Copeptin, a surrogate marker of the hormone arginine vasopressin (AVP) and the stable C-terminal portion of provasopressin, has been linked to declining kidney function in the general population. AVP testing is therefore helpful, but it is not frequently employed in clinical practice because of its extremely short half-life, which makes quantification challenging. Conversely, copeptin is easily detected immunologically and can be used as a vasopressin surrogate biomarker. This study aimed to investigate plasma copeptin in type 2 diabetic patients and to evaluate its potential utility as a diagnostic biomarker for the development of diabetic nephropathy. Methods: A case-control study that involved 52 individuals divided into two groups; 26 patients with type 2 diabetes and 26 normal subjects as a control group. Patients were subdivided into 2 subgroups; 13 patients with nephropathy and 13 patients without nephropathy. Investigations were serum creatinine, plasma copeptin, HbA1C, UACR. Results: Plasma copeptin levels were considerably elevated in diabetic patients with nephropathy than in those without (P< 0.001). Additionally, plasma copeptin showed a negative correlation with eGFR (P=0.005) and a positive correlation with serum creatinine, urea, and UACR (P=0.008, 0.014 and 0.005, respectively) in diabetic individuals with nephropathy. ROC curve analysis showed that serum copeptin at a cutoff point of 2pmol/l can be used to distinguish patients with and without diabetic nephropathy with a high sensitivity and a moderate specificity. Conclusion: Plasma copeptin levels are higher in diabetic individuals, especially in those who have nephropathy, and may serve as a biomarker for diabetic nephropathy diagnosis