Background: Multiple Sclerosis (MS) is a complicated neurological disorder. Imbalance and ataxic features are challenging symptoms in MS. Objective: To assess the effect of dual task on balance in ataxic MS patients. Methods: Thirty relapsing remitting MS patients, ataxic type, were assessed under two conditions: single task condition (A) for assessing balance and dual task condition (B)assessing balance while doing a motor task. Two types of motor dual tasks were chosen, "holding a tray task " and " coin transfer task". For balance assessment, Biodex Balance System (BBS) and Timed up and go (TUG) were used. Results: Condition (B) significantly change balance indices measured by BBS. Such changes were more pronounced under "coin transfer task" in comparison to "holding tray task". Moreover, there was increase in time of TUG-motor in comparison to TUG test. Conclusions: Motor dual tasks can affect balance of ataxic MS patients, such effects depend on secondary task difficulty. There are subclinical impairments that can be unmasked by reinforced balance assessment using motor dual tasks. Both static and dynamic balance assessments are considered complementary, its important to assess both to get a realistic evaluation.