Study aim: Pegylated interferon beta-1a (CinnaGen) is non-inferior to CinnoVex® (CinnaGen) for treatment of relapsing-remitting Multiple Sclerosis. Design: Phase III, randomized, parallel-group, and non-inferiority. The patient randomization process will be centrally conducted by simple randomization method (complete algorithm) in PASS software for a total of 168 patients (with a 1: 1 allocation ratio). After the randomization procedure, a code will be allocated to each patient that will be used as patient identifier throughout the study. Settings and conduct: The trial will be performed by principle and co-investigators in Tehran (Sina, Imam Hossein, and Amiralam hospitals), Isfahan (Kashani hospital), Mashhad (Ghaem hospital), Sari (Buali hospital), Tabriz (Imam Reza hospital) and Rasht (Ghaem hospital), Hamedan (Sina). Participants/Inclusion and exclusion criteria: Inclusion Criteria: Age 18-50 years, RRMS diagnosis, EDSS 0–5, At least one relapse within the past 12 months, Signed Informed Consent. Exclusion Criteria: Other types of MS, Surgery or treatment with other agents to treat MS symptoms or underlying disease as specified in the protocol, Abnormal screening lab tests, History of any medical condition that would preclude participation in the trial, MS relapse within 30 days prior to randomization and/or not stabilized from a previous relapse prior to randomization, Pregnancy and lactation, Unwillingness or inability to comply with the requirements of the protocol, The decision of the Investigator and Others specified in the protocol. Intervention groups: Group I: Pegylated interferon beta-1a (CinnaGen), Physioject™ autoinjector, 125mcg, subcutaneous, every 2 weeks for 96 weeks. Group II: CinnoVex® (CinnaGen), prefilled syringe, 30mcg, intramuscular, once a week for 96 weeks. Main outcome variables: The annualized relapse rate in a 96 weeks study period