This study investigated the effects of a static stretching (SS) program on muscle hardnesses of the gastrocnemius medialis (MG) and gastrocnemius lateralis (LG). Nineteen young men participated in this study. Either the right or left leg was randomly selected to conduct three bouts of 2‐min SS of the plantar flexors 6 days a week for 5 weeks in each subject (the SS group), and the other leg was assigned to a control group. Before (pretest) and after (posttest) conducting the SS program, MG and LG hardnesses were measured using shear wave ultrasound elastography. The SS program was found to decrease muscle hardnesses, but not to change the ratio of MG hardness to LG hardness. There were no significant differences between the relative changes in the MG and LG hardnesses from pretest to posttest in both the SS and control groups. Significant correlations between the muscle hardness ratios at pretest and posttest were found in both groups. The results of this study suggest that the current SS program is useful for improving muscle condition in the plantar flexors, and that its long‐term effects on the MG and LG hardnesses are of the same degree.