A decrease in the ability to maintain static and dynamic balance after stroke could be related to the inability to select reliable sensory information in producing relative motor action needed to maintain postural stability. The purpose of this study was to compare the effects of two different types of surface conditions on the balancing ability of subjects with stroke. Eighteen hemiparetic subjects were assigned to an experimental and control group participating in a six－week rehabilitative therapeutic exercise program focusing on balance and mobility. Exercises were performed 3 to 5 times per week in a stable surface condition by the control group, and in an unstable surface condition by the experimental group. Pre－ and post test assessments involved the measurement of the static balance and dynamic balance, respectively by 7－item Berg Balance Scale－3P and by Pro－3 Balance System. Results showed that under the unstable surface condition, static balance in the experimental group showed more improvement than that of the control group.(Statistically, not very significant.) All the aspects of dynamic balance and mediolateral sway(balance) improved significantly than those of the control group. However, there were no significant differences between two groups. Overall, it can be concluded that under the unstable surface condition, the rehabilitative therapeutic exercise programs are effective in improving the dynamic balance of stroke subjects. The results suggest that the adaptation of the unstable surface in the rehabilitative therapeutic exercises could be effective for the patients with hemiplegia in balance. Further studies are needed to confirm the effectiveness of the unstable surface on improving balance and postural stability of hemiplegics.