Purpose This study was to determine the effect of trunk training exercise on dynamic balance and energy expenditure during walk in chronic stroke patients. Methods This study used a single subject research design. Two chronic stroke patients were participated and received general training five times per week. The trunk training exercise program was modified from preceding studies and composed of trunk muscle strengthening and selective and coordinated movement. The subjects performed exercise program five times a week, forty minute a day, four weeks. Pre base line(A) was only collected participant information without intervention in 5 times. Trunk training exercise(B) was carried out 10 times and 5 times to base lime(A) after intervention. The dynamic balance of was evaluated by Timed Up and Go Test(TUG), the energy consumption was measured by the oxygen cost as the oxygen consumption per unit distance, energy expenditure index(EEI) as the difference of heart rate, in a session. Results The results of the evaluation in each subject were indicated that the dynamic balance test was improved, both oxygen cost and energy expenditure index were decreased during the intervention period. These effects were maintained even during the regression baseline period. Conclusion These results showed that trunk training exercise was effective in the improvement of dynamic balance and decrease energy consumption. This study suggests that trunk training exercise is effective in the improvement of energy efficiency during walk in chronic stroke patients.