Background: Handheld percussive massage guns are commonly used among athletes and healthy individuals. Objectives: The aim of this study was to examine the intervention effects by session of massage gun application on the gastrocnemius (GCM) muscle of healthy women and suggest an appropriate intervention time for massage gun on the calf muscle. Design: Single-group design. Methods: Thirteen healthy women in their 20s were recruited, and a massage gun was applied to the GCM muscle for 2 minutes per session for a total of 4 sessions. Changes in the muscle tone and stiffness of the GCM muscle and ankle range of motion (ROM) were analyzed by session. Results: After massage gun intervention, the muscle tone and stiffness of the medial gastrocnemius (MGCM) and lateral gastrocnemius (LGCM) muscles were significantly lower (P<.05). The active and passive ROM of the ankle joint significantly increased regarding both dorsiflexion and plantar flexion (P<.05). In terms of reduction of muscle tone and stiffness of the GCM muscle and increase of ankle ROM, the massage gun was most effective when applied for 4 sessions of 2 minutes each (P<.05). Conclusions: The use of a massage gun in healthy women in their 20s creates no physiological burden on muscle tone and stiffness of the GCM muscle and has an immediate effect on improving ankle joint movement. Therefore, there would be no particular problem in using a massage gun on the GCM muscle for self-care at home.