Objective: To investigate the effectiveness of botulinum toxin A (BTA) injection in lower extremities spastic muscles in stroke patients by quantitative ultrasound. Methods: A total of 22 adult stroke patients with lower limb spasm were included in the study and 20 adult healthy subjects as control group. The quantitative assessment of ultrasound was performed at preintervention, at 1-week postintervention and at 4-week postintervention., including mean grey value, (MGV), muscle thickness, fascicle length, pennate angle and shear wave elasticity (SWE) as well as clinical assessment including Brunnstrom staging and MAS. The difference of ultrasonic quantitative parameters of muscles between stroke group and healthy group and the changes of spastic muscles in stroke patients before and after botulinum toxin injection treatment were compared. The relationship between quantitative parameters of ultrasound and clinical evaluation scales was analyzed.Results: Muscle thickness and fascicle length of medial gastrocnemius (MG) in stroke group were significantly decreased than those in healthy group. The MGV and Young’s modulus of MG and soleus (SL) in stroke group were significantly increased compared with those in healthy group (P ＜ 0.05). After 1 week and 4 weeks of treatment compared with the baseline values, significant improvement was observed in Young’s modulus of MG and SL (P ＜ 0.05). Positive correlation was observed between The Young’s modulus of MG with MAS score in stroke patients(r=0.519, P ＜ 0.05). The value of MGV was positively correlated with the efficiency of treatment(r=0.435, P ＜ 0.05).Conclusion: Quantitative ultrasound can provide information about spastic muscles after stroke and is a promising diagnostic tool for evaluation and follow-up in spastic muscles after BTA injection treatment