Summary Background and Purpose: Studies have unanimously supported that left-hemisphere specialization is greater than the right hemisphere for representation of learned actions and motor learning, but it is not clear as to whether there is a particular specialization related to motor programming. This study investigated the issue by comparing the effect of transcranial direct current stimulation (tDCS) of the primary motor cortex (M1) on the right and left hemispheres. Methods: Participants (n=53) practiced special motor patterns for a period of three days and the left M1 and right M1 groups received simultaneous stimulation in the left and right M1, respectively. Data obtained from root mean square (RMS) error, movement time, RMS error/movement time ratio, and skill were analyzed using repeated measures ANOVA. Results: The results showed that although all groups experienced a significant reduction in RMS error over time relative to the pretest stage (P <0 .05), the left M1 group had significantly lower RMS error only in the retention stage compared with the other groups (P <0. 05). Also, the results showed that the progress rate in skill factor was greater in the left M1 group than in the right M1 and control groups. Conclusions: The left hemisphere is probably more specialized in motor programming, and this laterality is expected to be through the motion-consolidation mechanism

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