Introduction: Walnut leaf contains large amounts of antioxidants, phenolic compounds and flavonoids and the beneficial effect of these compounds in the treatment of diabetes has been shown. This study investigated the effect of cyclohexane and ethanol extract of walnut leaf on activity of sorbitol dehydrogenase (SDH) enzyme. Methods: Fifty-six adult male Sprague-Dawley rats were divided into seven groups and treated for 30 days as follows: control and diabetic control (received sesame oil as vehicle), control cyclohexane & control ethanol (received 250 mg/kg body weight of cyclohexane and ethanol extracts respectively), diabetic cyclohexane 250 (received 250 mg/kg cyclohexane extract), and diabetic ethanol 150 & diabetic ethanol 250 (received 150 and 250 mg/kg ethanol extract respectively). Diabetes was induced by single injection of streptozotocin (60 mg/kg, ip). Body weight and blood glucose were recorded weekly and in the last day of treatment animals were sacrificed by whole blood collection directly from the heart. Activity of SDH was measured in the serum by ELISA method. Results: Oral administration of cyclohexane extract of walnut leaf at a dose of 250 mg/kg in the diabetic group improved blood glucose significantly compared to other diabetic groups. Administration of both extracts reduced activity of SDH compared to diabetic control group significantly. There was no significant difference of body weight between treatment groups and diabetic control group at the end of the treatment period. Conclusion: Cyclohexane extract of walnut leaf decreased blood glucose significantly, while both extracts reduced activity of SDH significantly in diabetic animals.