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Objective: To observe the effect of complexity of unilateral hand activity or dominance of hand on ipsilateral motor cortex excitability. Method: Twenty healthy volunteers of right handedness were recruited. We applied the transcranial magnetic stimulation on right hemisphere, and measured motor evoked potential (MEP) at left first dorsal interossei (FDI). We observed the changes of MEP amplitude during the execution of three different complexities of right finger movement. We set the motor tasks as (1) relaxed state, (2) repetitive opposition of 3rd finger (simple exercise) and (3) opposition of 3rd, 5th, 2nd, 4th finger (complex exercise). These tasks were performed within one minute, and repeated 3 times. To observe the effect of hand dominance, we also measured MEP at right FDI during left hand movements. Results: Ipsilateral motor cortex was significantly facilitated by ipsilateral voluntary hand activity (p<0.01). And the MEP amplitude was also increased by complexity of hand exercise. Conclusion: We found that the excitability of ipsilateral motor cortex was changed by unilateral hand exercise, and the excitability was increased by complexity of hand exercise.