Introduction This study aims to investigate the effect of botulinum toxin-A (BoNT-A) injection into pectoralis major and teres major muscles and suprascapular nerve block (SSNB) on pain, range of motion (ROM), and upper extremity function for (hemiplegic shoulder pain) HSP, and to compare the effectiveness of these two methods. Materials and methods Sixty patients with HSP were randomly assigned into 2 groups. The Group 1 (n = 30) received BoNT-A injection into the pectoralis major and teres major, and the Group 2 (n = 30) received SSSB. Patients were evaluated just before the start of the study, and 2 and 6 weeks after the start of the study with visual analog scale (VAS), Modified Ashworth Scale (MASH), the passive ROM, and the Fugl-Meyer Scale (FMS) arm section. Results In Group 1, statistically significant improvement was found in all evaluation parameters on 2th and 6th week. Group 2 showed significant improvement in all parameters on week 2 (p < 0.05), and significant improvement was observed in MASH and pain in abduction in the 6th week (p < 0.05). When the groups were compared with each other, a statistically significant difference was observed in MASH, ROM, and FMS parameters on week 2 in favor of Group 1; in all evaluation parameters, there was a statistically significant difference in favor of Group 1 on week 6 (p < 0.05). Conclusion We concluded that BoNT-A injection into the pectoralis major and teres major muscles for HSP was equal in the short term and more effective in the middle term compared with SSNB treatment in improving pain, ROM, and function.