Background: As ways to optimize the mobilization of postural stability muscles for sitting up motions, arm reaching motions and head raising motions have important effects. Objectives: This study was conducted to investigate the effects of reaching to sit-up training on the trunk muscle activity, postural ability, and balance ability of patients with hemiplegia due to stroke. Design: Randomized controlled trial. Methods: This study was conducted with 18 stroke patients who met the selection criteria divided into two groups: a study group of 9 patents and a control group of 9 patients. The study group carried out reaching to sit-up training, which can promote trunk muscles and improve control through trunk interactions. The control group received general physical therapy intervention Results: The activity of the trunk muscle was significantly different before and after intervention in study and control group. The functional reaching test showed significant changes in both the study group and the control group. The timed up and go test showed a significant change in the study group. Conclusion: Reaching to sit-up training for 4 weeks showed increases in trunk muscle activity in stroke patients and was effective in improving balance ability.