The rat exhibits various kinds of rhythmical jaw and lip movements, during such as chewing, drinking, and grooming. To examine co-ordination between jaw and lip movements, we compared activities of jaw and orbicularis oris (OO) muscles recorded from freely moving rats. The following results were obtained: 1) During chewing, activities of the OO muscle synchronized with those of the jaw opening muscle. Magnitude of OO muscle activity decreased with hardness of food, while that of jaw muscles increased. 2) During grooming (licking body surface), activities of the OO muscle did not synchronized with those of the jaw opening muscle. Magnitude of OO muscle activity was always greater than that of the jaw opening and closing muscles.