Background: Nonalcoholic fatty liver disease (NAFLD) as a metabolic disorder has a high prevalence. Increasing serum concentrations of liver enzymes, lipid profiles, and fasting blood sugar (FBS) are the most laboratory findings in NAFLD. Efforts to identify effective treatments with fewer side effects to address these impairments are increasing. Grape seed extract (GSE) is rich in antioxidants (eg, proanthocyanidins (Pas), which it has beneficial effects reported previously). Objectives: We evaluated the effect of GSE on biochemical markers in NAFLD patients. Methods: The current randomized, double-blind clinical trial was investigated the GSE effect on patients with NAFLD. The patients were assigned into 2 groups (GSE and control groups). The duration of treatment was considered 2 months. The GSE group received GSE capsules (200 mg, two times a day for 2 months), and the control group received placebo (200 mg starch). The serum concentration of aspartate aminotransferase (AST), triglyceride (TG), FBS, high-density lipoprotein (HDL), alanine aminotransferase (ALT), low-density lipoprotein (LDL), and cholesterol were assessed at baseline, 1 month, and 2 months after treatment. Body mass index (BMI) and HDL/LDL ratio were assayed at different times. Results: The levels of AST, ALT, FBS, TG, HDL, LDL, and cholesterol significantly decreased, (P-value < 0.05), and the level of HDL significantly increased in patients who received GSE 200 mg twice a day for 2 months (P-value < 0.05) compared to control group, but BMI and weight did not change significantly (P-value > 0.05). Conclusions: Grape seed extract can be effective in fatty liver patients; such results may be contributed to the antioxidant properties of GSE due to the high amount of PAs and similar constituents in GSE. However, more investigations are needed to clarify the exact involved mechanism of GSE.