OBJECTIVE: Spasticity developing in the upper extremity in stroke patients causes disability by limiting movement and causing pain. This study investigates the effects of botulinum toxin injections on pain, functionality, spasticity, and range of motion in hemiplegic patients with post-stroke spasticity. MATERIALS AND METHODS: The study involved a double-blind, prospective, randomized controlled trial with thirty-one stroke patients aged 35-80 who developed upper extremity spasticity. The study group (n=16) received botulinum toxin-A (BT-A) injections in addition to conventional rehabilitation and stretching exercises, while the control group (n=15) received placebo injections. Evaluations were conducted before treatment, in the second week, and three months after treatment. The study evaluated pain relief through the Visual Analog Scale (VAS), assessed spasticity with the Modified Ashworth Scale (MAS), and measured functionality using the Fugl Meyer Assessment Scale (FMAS) and the Box Block Test (BBT). RESULTS: The mean age of patients was 56.03±11.81. The median time after stroke was 24 months. The BT-A group demonstrated significantly lower VAS and MAS scores compared to controls at both 2 weeks and 3 months after treatment. Additionally, the BT-A group showed significantly higher changes in arm, wrist, and total FMAS scores compared to the control group. However, no significant difference was found in terms of hand, coordination, and speed FMAS score changes. CONCLUSIONS: The results of our study demonstrated that BT-A injection with ultrasonography guidance is an effective method for alleviating pain caused by passive shoulder movement, significantly reducing spasticity, and markedly improving motor functions.