Study aim: The aim of this study is to determine the effects of probiotic supplementation on disease severity, mental health, insulin resistance, inflammatory factors and biomarkers of oxidative stress in patients with multiple sclerosis. Design: Parallel double-blind (both patients and researchers) randomized controlled clinical trial. Random assignment will be done by the use of computer-generated random numbers. 48 patients with multiple sclerosis of eligible in the study will be selected. Patients will be assigned to receive either probiotic supplements and placebo. Fasting blood samples will be taken at baseline and after 16-wk intervention. Settings and conduct: Patients with multiple sclerosis of eligible and referred to Beheshti Clinic affiliated to Kashan University of Medical Sciences, Kashan, Iran in the study will be selected. Participants/Inclusion and exclusion criteria: The inclusion criteria were patients with ages between 20 and 60, course of disease relapsing–remitting MS (RRMS), identified according to McDonald criteria and an expanded disability status scale (EDSS) score ≤4.5 referred to the Neurology Clinic of Shahid Beheshti Hospital in Kashan city, Iran. The exclusion criteria were primary progressive MS (PPMS), secondary progressive MS (SPMS), clinical relapse and glucocorticoid therapy during the past one month, pregnancy, women who were lactating within the prior six month, patients with bearing nephrolithiasis within the prior five years and consumers of probiotic or synbiotic during the past three month. Intervention groups: Patients will be assigned to receive either probiotic supplements (intervention group: n=24) and placebo (control group: n=24). Main outcome variables: Disease severity, mental health, insulin resistance, inflammatory factors and biomarkers of oxidative stress will be measured at study baseline and end-of-trial