Purpose: The purpose of this study was to evaluate the electromyographic (EMG) activity of vastus medialis oblique (VMO) and vastus lateralis (VL) muscles on foot position and knee angle for hemiplegia patients. Methods: Ten stroke subjects (10 males) participated in the study. Subjects were all right-hemiplegic patients. All subjects did $0^{circ},;20^{circ}$ and $40^{circ}$ knee flexion while maintaining the foot in a neutral position, or at $30^{circ}$ adduction or at $30^{circ}$ abduction. Surface EMG data were collected for VMO and VL muscles on the non-hemiplegic side and hemiplegic side. Collected data were analyzed using two-way ANOVA. Results: VMO and VL activities for the non-hemiplegic and the hemiplegic sides were highest for $40^{circ}$ knee flexion while maintaining the three foot positions. There were no significant differences in EMG activity of the VMO and VL muscles with different foot positions. There were significant differences between VMO and VL activity for knee flexion angle while maintaining the foot in neutral (p<0.05), at $30^{circ}$ adduction (p<0.05), or at $30^{circ}$ abduction (p<0.05). Conclusion: Foot position does not influence VMO and VL activities. But, knee flexion exercise in a closed chain can increase VMO and VL muscle activity for hemiplegic patients. In particular, VMO and VL activities for both the non-hemi side and the hemi side were highest for $40^{circ}$ knee flexion.