Objective : The purpose of this study was to evaluate the changes in the upper extremity function and trunk muscle activity from stable supporting surfaces in patients with stroke-induced hemiplegia. Methods : Fifteen hemiplegic patients (9 male, 6 female) who attended the ○○ rehabilitation hospital in D Metropolitan participated in this study. Their level of upper extremity function was measured using a multidimensional bimanual coordination KEPAD work sample test. Their trunk muscle activity (internal oblique, external oblique, and erector spinae), depending on changes from the use of stable supporting surfaces, were measured using surface electromyography. Results : The differences in the level of upper extremity function and trunk muscle activity while being seated were compared for three surface supports. Their level of upper extremity function while seated was significantly different when support was provided for both sides and for the affected side. However, there was no significant difference when the support was provided for both sides and when the support was provided for the unaffected side. Their trunk muscle activity while seated was not significantly different among the three types of support surface. Conclusion : The results of this study showed that support to both sides of hemiplegic patients while in a sitting position affects their upper extremity function. Occupational therapy for hemiplegic patients in the form of repetitive training to support both sides can enhance the functional movement of their upper extremities.