The purpose of this study was to investigate the changes of masticatory movement, maximum bite force, and labial-closure-strength after masticatory exercise using hard chewing gum for 1 month. The subjects were 13 children (9 girls, 4 boys; average age, 10.5y) with mixed dentition. The subjects practiced for 10 minutes twice/day for a period of 1 month. Chewing gum was used as the test product to conduct masticatory exercises. Jaw movements such as the opening and closing paths angle and masticatory width of the frontal plane on the habitual chewing side, number of masticatory cycles, and changes in right and left chewing sides were measured. Maximum bite force on the habitual chewing side and labial-closure-strength were also measured. Data were taken before starting exercises (T1), immediately after commensing exercises (T2), and 1 month after exercises (T3). There were significant differences between T1 and T2 in masticatory width, closing paths angle, number of masticatory cycles, changes in right and left chewing sides, maximum bite force, and labial-closure-strength. Furthermore, there were significant differences between T1 and T3 in masticatory width, changes in right and left chewing sides, maximum bite force, and labial-closure-strength. On the contrary, however, there was no significant difference in these parameters between T2 and T3. In conclusion, this study indicates that masticatory function is improved by masticatory exercises and that the beneficial effects were maintained ≤1 month after completion of masticatory exercises.