Background: To investigate the effect of high-voltage alternating current (AC) electric field exposure on muscle extensibility. Methods: The study design was a crossover comparison. Fifteen healthy men were randomly divided into two groups. The interventions were exposure and no exposure to a high-voltage AC electric field (18 kV, 30 min). Subjects then performed bilateral self-stretching of the trapezius, hamstrings, and rectus femoris. Skin temperature, blood flow rate, blood pressure, heart rate, muscle rigidity, and muscle extensibility were measured before and after the intervention, and muscle rigidity and muscle extensibility were measured again after stretching. Skin temperature was measured bilaterally on the palms, shoulder girdle, anterior thigh, and dorsum of foot. Blood flow rate was measured in the right radial artery and dorsal artery of the foot. Muscle rigidity was measured bilaterally in the trapezius, rectus femoris, and biceps femoris. Muscle extensibility indices were determined for the left and right angle of lateral neck flexion, heel-buttock distance, straight leg raise angle, and sit-and-reach distance. Skin temperature, blood flow rate, blood pressure, and heart rate were compared between before and after the intervention, and muscle rigidity and muscle extensibility were compared before and after the intervention and after stretching. Results: A significant improvement was found in muscle extensibility in the intervention group but not in the controls. Muscle extensibility improvements due to stretching were noted regardless of electric field exposure, but the degree and percentage of change in muscle extensibility was significantly higher after stretching following electric field exposure. Electric field exposure had no effect on muscle rigidity or circulatory dynamics. Conclusions: Exposure to the high-voltage AC electric field appeared to increase muscle extensibility and heighten the effect of stretching. However, as the mechanism for improved muscle extensibility due to high-voltage AC electric field exposure was not clear, further study is necessary.