Motor evoked potential (MEP) activated by transcranial magnetic stimulation are useful to direct evaluation of corticospinal motor system. This method is non-invasive, painless and is not attenuation by physiologic barrier such as skulla scalp. In this study, central motor conduction time (CMCT) and ampltude of affected side in 30 hemiparetic paitients were compared with unaffected side. There was no difference in CMCT between unaffected side and normal value but significantly delayd between affected side and normal value (p<0.025). The amplitude was also significantly decreased between normal side and affected side (p<0.025). The difference of %CMCT and %Amplitude (the paretic side as a function of responses elicited from the intact side) were highly significant (p<0.005). And the correlation between the degree of muscle maneuver test and evoked potential were -0.65 (%CMCT), 0.58(%AMP), 0.69(CMCT)(p<0.005). There was no unwanted side effects in this study. And in our study, the motor evoked potentials activated by transcranial magnetic stimulation is useful method to evaluate the patients with motor weakness induced by brain pathology, especially above grade 3 of muscle test.