Pharmaceutical. compositions comprising a pynmidine synthesis inhibitof, process of preparation thereof and method of using the same are provided. Particularly the. present invention ˜relates to pharmaceutical compositions comprising tfiflunomide, process of preparation thereof and method to treat patients suffring from autoimmune diseases in particular systemic lupus>erythematosus or graft-yersus-host diease or rheumatoid arthritis or multiple sclerosis.