Background: Nonalcoholic fatty liver disease (NAFLD) is a chronic liver condition complicating type II diabetes. Insulin resistance (IR) plays a vital role in the pathogenesis of fatty liver in diabetes mellitus. Interestingly, both w-3 polyunsaturated fatty acids (w-3 PUFA) and apelin-13 have controversial relationship to IR and liver function. Objective: To demonstrate the effect of w-3 PUFA on serum apelin-13 and its association to liver function in type II diabetic rats. Material and methods: This study was conducted on 40 of  adult male albino rats divided into 3 groups: Control group (A) in which rats fed normal chow, type II diabetic group (B) in which type-II diabetes was induced by feeding the rats HFD for 2 weeks followed by a single intraperitoneal injection of streptozotocin (35 mg/kg BW), and type II diabetic treated group (C) in which rats treated with ω-3 PUFA (500mg/kg/day; orally) for 4 weeks after induction of diabetes. Results: There was a significant elevation in serum apelin-13, glucose, HOMA-IR, ALT, AST, plasma prothrombin and fibrinogen accompanied by significant decrease in serum insulin and albumin in group (B) when compared with control group. Treatment with PUFA in group (C) improved gluco-lipid metabolic parameters with significant reduction in serum apelin-13, ALT and AST. Linear regression analysis test showed that apelin-13 has no predictive value to the histological changes of liver injury in group B. Conclusion: Treatment of diabetic rats with w-3 PUFA improved insulin resistance, liver enzymes and decreased serum apelin-13 level. However, apelin-13 cannot be used as a non invasive laboratory marker to distinguish the severity of liver injury in type II diabetic rats.