OBJECTIVE: To identify the effects of isokinetic strengthening of trunk muscles on balance in hemiplegic patients after stroke. METHOD: All participants were ambulatory hemiplegic patients, injured at least 6 months prior to study. The patients (n=16) were randomly divided into two groups. The control group received neurodevelopmental treatments and gait training 3 times a week. In addition to the same treatments provided for the control group, the experimental group received trunk isokinetic strengthening exercises using isokinetic dynamometer 3 times a week. Trunk muscle peak torque and balance in the experimental group were compared with those in control group at baseline and 4 weeks after treatments. RESULTS: There were no significant differences in age, lesion of hemiplegia, time after stroke onset, trunk muscle strength and Berg balance score before treatments between two groups. In the experimental group, peak torques of trunk extensor increased significantly at 60degrees/sec and 90degrees/sec at 4 weeks (p<0.05), but there were no significant improvements in peak torques of trunk flexor at all degree and extensor peak torques at 120degrees/sec. Both the extensor and flexors showed no significant changes in the control groups. In the experimental group, a mean percent change in peak torque involving the trunk extensor was significantly increased at 60degrees/sec. In the experimental group, Berg balance scores, 10 m gait velocity, sit to stand and gait 3 m and return, and 10 seconds stair up and down were improved (p<0.05). No significant improvements were noted in the control group. CONCLUSION: Isokinetic strengthening of trunk muscles can improve balance in hemiplegic patients.