Transcranial direct current stimulation(t DCS), an emerging technique for non-invasive brain stimulation, is increasingly used to induce changes in cortical excitability and modulate motor behavior, especially for upper limbs. The purpose of this study was to investigate the effects of t DCS of the primary motor cortex on visuomotor coordination based on three levels of task difficulty in healthy subjects. Thirty-eight healthy participants underwent real t DCS or sham t DCS. Using a single-blind, sham-controlled crossover design, t DCS was applied to the primary motor cortex. For real t DCS conditions, t DCS intensity was 1 m A while stimulation was applied for 15 minutes. For the sham t DCS, electrodes were placed in the same position, but the stimulator was turned off after 5 seconds. Visuomotor tracking task, consisting of three levels(levels 1, 2, 3) of difficulty with higher level indicating greater difficulty, was performed before and after t DCS application. At level 2, real t DCS of the primary motor cortex improved the accurate index compared to the sham t DCS. However, at levels 1 and 3, the accurate index was not significantly increased after real t DCS compared to the sham t DCS. These findings suggest that tasks of moderate difficulty may improve visuomotor coordination in healthy subjects when t DCS is applied compared with easier or more difficult tasks. Transcranial direct current stimulation (t DCS), an emerging technique for non-invasive brain stimulation, is increasingly used to induce changes in cortical excitability and modulate motor behavior, especially for upper limbs. The purpose of this study was to investigate the effects of t DCS of the primary motor cortex on visuomotor coordination based on three levels of task difficulty in healthy subjects. Thirty-eight healthy participants underwent real t DCS or sham t DCS. Using a single-blind, sham-controlled crossover design, t DCS was applied To the primary motor cortex. For DCS, t DCS intensity was 1 m A while stimulation was applied for 15 minutes. For the sham t DCS, electrodes were placed in the same position, but the stimulator was turned off after 5 seconds . Visuomotor tracking task, consisting of three levels (levels 1, 2, 3) of difficulty with higher level indicating greater difficulty, was performed before and after t DCS application. At level 2, real t D CS of the primary motor cortex improved the accurate index compared to the sham t DCS. However, at levels 1 and 3, the accurate index was not significant increased after t DCS compared to the sham t DCS. difficulty may improve visuomotor coordination in healthy subjects when t DCS is applied compared with easier or more difficult tasks.