Semaphorin 3A (Sema3A) as an immune modulator could participate in the pathogenesis of autoimmune diseases. In the current study, we aimed to investigate Sema3A expression in peripheral blood mononuclear cells (PBMCs) and its serum level in relapsing-remitting multiple sclerosis (RRMS) patients. Fifteen newly determined and untreated RRMS patients were chosen and assessed in relapsing and remitting phases in compare with fifteen healthy individuals. In consistent with previous findings in other autoimmune diseases, our results revealed that serum level of Sema3A and its expression in PBMCs of RRMS patients were significantly lower than in normal subjects. We also evaluated this down regulation predictive value with ROC analysis. According to our data, we suggest that Sema3A could be involved in pathogenesis of MS and might be a potential diagnostic biomarker for the disease. (C) 2017 Elsevier B.V. All rights reserved.