OBJECTIVE:Multiple Sclerosis (MS) is one of the most common neurological diseases in the world. Due to structural and functional changes in central nerves system, the patients with MS may affected by sensory-motor learning deficits. The aims of the current study was to assess the effect of primary motor cortex (M1) anodal transcranial direct current stimulation (a-tDCS) on online and offline motor learning in patients with MS. MATERIALS AND METHODS:Thirty-nine patients with MS were randomly assigned in three groups: concurrent M1 a-tDCS and serial response time test (SRTT) (n=13), concurrent sham a-tDCS and SRTT (n=13) and SRTT-only control (n=13). The participants in all groups were asked to concurrently perform 20 minutes of SRTT. M1 a-tDCS group received 20-minute M1 a-tDCS (2 mA) concurrent with SRTT, while the a-tDCS was turned off after 30 seconds in the sham a-tDCS group. Response time (RT) and error rate (ER) during SRTT were assessed prior, during and 48 hours after the intervention. RESULTS:Online learning happened in all groups (P < 0.05), with more significant learning in M1 a-tDCS group as compared to the other groups (P < 0.05). However, offline learning was occurred only in M1 a-tDCS group (P < 0.05). CONCLUSIONS:The findings indicate offline motor learning impairment in patients with MS. M1 a-tDCS may be used for enhancement of motor learning especially offline learning in patients with MS.