CONTEXT: Non-alcoholic fatty liver disease (NAFLD) is a chronic liver disease, with 5-10% of liver having extra fat. Increase in its prevalence in all age groups is linked with obesity and Type II diabetes. The treatment of NAFLD remains controversial. A growing body of evidence suggests a relation between overgrowth of gut microbiota with NAFLD and non-alcoholic steatohepatitis (NASH). The objective of this review is to provide an overview on experimental and clinical studies assessing all positive and negative effects of probiotics. EVIDENCE ACQUISITION: We made a critical appraisal on various types of documents published from 1999 to March 2012 in journals, electronic books, seminars, and symposium contexts including Medline, PubMed, and Cochrane Central Register of Controlled Trials databases. We used the key words: "non-alcoholic fatty liver disease, probiotics, non-alcoholic steatohepatitis, liver disease, and fatty liver". RESULTS: Probiotics, as biological factors, control the gut microbiota and result in its progression. It is in this sense that they are suggestive of a new and a natural way of promoting liver function. Correspondingly, limited evidence suggests that probiotics could be considered as a new way of treatment for NAFLD. CONCLUSIONS: Various experimental studies and clinical trials revealed promising effects of probiotics in improving NAFLD; however given the limited experience in this field, generalization of probiotics as treatment of NAFLD needs substantiation through more trials with a larger sample sizes and with longer-term follow up.