Objective To investigate the underlying mechanism of motor recovery of the hemiplegic lower extremity in stroke patients. Methods The brain activation pattern during sequential extension-flexion of the affect-ed knee of 7 stroke patients and 8 healthy subjects was observed by blood-oxygen- level-dependent fMRI (BOLD-fM-RI) and analyzed by microsoft SPM5. Results When executing unilateral knee flexion-extension, contralateral paracentral lobe and contralateral supplementary motor area and right temporal gyms and inferior parietal lobes of both sides were significantly activated in all the healthy subjects, while the ipsilateral parietal lobe BA7 and BA5 were sig-nificantly activated in 6 of the 7 stroke patients. Conclusions Sequential extension-flexion of the affected knee of stroke patients was probably dependent on the activation of BA7 and BA5 in the intact side. Compensatory activation of the intact hemisphere might be one of the main mechanisms for the paretic lower extremity motor recovery in stroke patients.