<p>This study aimed to investigate the tissue elastic properties of the orbicularis oris muscle inferior during physical growth and development in children. The orbicularis oris muscle inferior was examined at rest and during muscle contraction generating maximal tensile force (MCT) through a button-pull exercise using sonographic elastography. The inclusion criteria for participants were the absence of organic disorder in the orbicularis oris muscle and the presence of stable occlusion. A total of 146 participants (77 males and 69 females) aged 4–17&#xa0;years were included. The strain ratio of the orbicularis oris muscle inferior was measured at rest and during MCT, and the average values for each age were calculated. The average strain ratio for all ages was 0.77 ± 0.15 at rest and 1.22 ± 0.29 during MCT through a button-pull exercise. The average strain ratio of the orbicularis oris muscle inferior at rest ranged from 0.67 to 0.87 across all ages, whereas that during MCT through a button-pull exercise ranged from 1.14 to 1.36. The tissue elasticity of the orbicularis oris muscle inferior in children was found to remain almost constant at rest and during MCT, regardless of age. These findings indicated that tissue elasticity was stable and that the average strain ratio at rest and during MCT can be used to evaluate perioral muscles, particularly the orbicularis oris muscle inferior in the maxillofacial region during physical growth and development in children.</p>