This study aims to evaluate the effect of extracorporeal shock wave therapy (ESWT) on lower limb spasticity in stroke patients. Twenty-eight eligible patients with ankle plantar flexor spasticity were randomly assigned to two groups. ESWT group received 1 session per week for 3 weeks of ESWT along with oral anti-spastic medications and stretching exercises. The control group received only oral anti-spastic medications and stretching exercises similar to ESWT group. At baseline, weeks 1, 3 and 12, spasticity was assessed and compared between the two groups using Modified Ashworth Scale (MAS), clonus score, passive range of motion (ROM) of joint, pain score, 3-m walk duration and lower extremity functional score (LEFS). Three patients were lost during follow-up; 25 patients completed the study and were analyzed. After one session of ESWT treatment, MAS, pain, ROM and LEFS improved significantly compared to baseline. After three weeks of ESWT treatment, MAS, pain and 3-m walk duration improved significantly compared to week 1. At week 12, MAS, pain, ROM, 3-m walk duration and LEFS improved significantly compared to the control group after controlling baseline values. The trend of decrease in pain score and MAS was significantly different between the groups. The trend of increase in ROM and LEFS was significantly different between the groups. ESWT significantly improved lower limb spasticity, pain, passive ROM, 3-m walk duration and LEFS immediately and 12 weeks after treatment. So, ESWT in combination with oral anti-spastic medications and stretching exercises could be useful for improvement of spasticity in stroke patients.