Melatonin has shown promising effects in controlling the progress of non-alcoholic fatty liver disease (NAFLD), introducing it as a possible candidate for NAFLD treatment. In this context, the current study is aimed to evaluate melatonin's effect on the plasma levels of Gamma-glutamyl transpeptidase, cholesterol, triglyceride, and liver aminotransferases in NAFLD patients. NAFLD and melatonin, as well as their related terms, were searched in electronic databases, until May 1st, 2020. The initial search identified 1152 studies. Considering inclusion and exclusion criteria, the final seven articles were included in the study. The methodology of the articles was assessed by the Newcastle-Ottawa Scale. Alanine transaminase levels were significantly lowered with melatonin treatment but not earlier than the 4th week (P = 0.010 and 0.519, respectively). Aspartate aminotransferase levels didn't show significant alteration before 4 weeks, although exhibiting substantial decline in total (P = 0.697 and 0.008, respectively). Alkaline phosphatase changes under 4 weeks of follow-up were not significant (P = 0.3), however, it decreased significantly in total (P = 0.006). A significant decline was detected in triglyceride levels after melatonin treatment (P = 0.015). There was a significant reduction in cholesterol levels (P = 0.005). Gamma-glutamyl transpeptidase levels were also significantly different after the administration of melatonin (P < 0.001). Melatonin could reduce the progress of NAFLD. It might also decrement hepatic function parameters. Thus, it could be used for managing NAFLD and possibly as part of the treatment plan for patients with NAFLD.