Objective To evaluate the effect of botulinum toxin type Ain the treatment of masseteric hypertrophy.Methods From August 2005 to January 2014,15 women with masseteric hypertrophy were enrolled in this study.Fifty units of botulinum tosin type A was injected bilaterally in the masseter muscles .The thickness of masseter muscles was measured preoperatively,4,12 and 24 weeks postoperatively using B-ultrasound .Results All the patients were followed up for 6 months.The mean reduction of masseter muscle thickness were （15.60±4.96%）at 4 weeks and （27.72±9.13）%at 12 weeks postoperatively.The percent of reduction decreased to （24.32±8.86）%at 24 weeks postoperativelyl.Conclusion Botulinum toxin type Ais effective in treating hypertrophy of the masster muscle .B-ultrasound could effectively reflect the reduction of muscle thickness after botulinum toxin type A injection.