Background: Masticatory movement occurs complicatedly and bilaterally. Although the tongue plays an important role in mastication, bilateral tongue function during mastication has not been clarified yet. Objective: To investigate the effect of food properties on posterior tongue activity and coordination of muscles bilaterally by electromyography (EMG). Methods: Twenty healthy adults (10 males and 10 females; mean age 28 years; range: 22-33 years) participated in this study. Three test foods, gummy jelly (hard food), sponge cake (soft food requiring crushing), and mashed potatoes (soft food not requiring crushing), were used. Bilateral masseter N-EMG (surface electromyography for measuring the muscle activity of posterior tongue) and submental EMG were carried out while the participants chewed three test foods. The participants were instructed to masticate three test foods only on the right side and only on the left side unilaterally. Results: In the case of gummy jelly, N-EMG activity on the mastication side was significantly larger than that on the non-mastication side (P <.01). Regarding temporal relationship between the masseter and N-EMG activity, in the case of gummy jelly, the percentage of cases where the N-EMG peak was observed during masseter muscle EMG bursts was significantly higher than those for sponge cake and mashed potatoes (P <.01). Conclusion: N-EMG activity on the mastication side was significantly larger than that on the non-mastication side in the mastication of hard foods. Tongue showed activity pattern changes and coordinated with the masseter muscle depending on food texture.