This study aimed to clarify the temporal and quantitative modulation in the orbicularis oris (OO) and buccinator (BUC) muscle activities during mastication. Ten healthy males (26.9 ± 1.0 years) participated. Electromyograms (EMGs) of the facial muscles were recorded with fine wire electrodes when chewing the chewing gum (one to four sticks) and peanuts (one to five pieces). Surface EMGs of the masseter (MAS) and digastric muscles were recorded simultaneously. EMGs of the OO and BUC showed rhythmic single-peaked bursts corresponding to the jaw-opening phase of chewing cycles. The total cycle lengths were constant regardless of the food amount. Integrated EMGs of the OO changed significantly when the amount of both foods changed (ANOVA: P<0.05). Those of the BUC changed significantly with the amount of gum changed (P<0.05), but did not change with the amount of peanuts changed. The burst duration of OO changed significantly when the amount of gum changed during ipsilateral chewing (P<0.05). When the amount of peanuts changed during ipsilateral chewing, the onset of OO and the peak of BUC based on the onset of MAS activity changed significantly (P<0.05). However, the onset, peak and offset of the OO and BUC based on the offset of MAS did not change regardless of the amounts chewed. The changes of the OO and BUC activities may derive from chewing-generated sensory inputs in accordance with the physical property of food in part, which would relate to the function of these muscles during mastication.