Introduction The aim of this study was to investigate the functional changes in the upper extremity of the intact side of hemiplegic patients within 0-12 months after stroke. Material and methods The study included 32 individuals with Stage 3 and Stage 4 progression according to Brunnstrom stages, whose right side was dominant. The age range of the individuals in the study was 45-80 years. This research was a prospective study planned according to the single group pretest-post test pattern. There was no control group. Results As a result of the study, it was determined that pain increased in the shoulder region of the non-affected side during the one-month follow-up period and therefore, upper extremity functionality decreased. After one month, strength values of grip, shoulder flexion (left intact), shoulder extension, shoulder abduction (right intact), shoulder internal rotation, shoulder external rotation (left intact), elbow flexion, elbow extension, and wrist extension increased. Furthermore, during this follow-up period upper extremity functionality decreased, pain values increased in the shoulder area, and hand grip strength values increased in individuals whose disease duration was 0-6 months and 7-12 months. Conclusions The non-affected upper extremity of a stroke patient plays an important role in helping them throughout the activities of their daily life. This study concluded that, upper extremities of the non-affected side of hemiplegic patients are also affected in terms of muscle strength, pain and functionality.