Many aspects of the coordination of lip and mandibular movements in the process of eating have not yet been clarified. This time, aiming to objectively evaluate lip and mandibular movements when chewing, the movements of the corners of the mouth and the mandible during mastication were measured three-dimensionally and analyzed. The subjects were 20 healthy women with individual normal occlusion. The test food was a commercially-available biscuit with a weight of 1 g. With six measuring points set for the lips and pogonion, the movements at those measuring points were captured with two CCD cameras during mastication, and the resulting images were analyzed with a three-dimensional motion analysis system. The analysis result showed that X- and Z-axis movements occurred on the working-side corner of the mouth, with Z-axis movements preceding X-axis movements, while on the balancing-side corner of the mouth, X- and Z-axis movements occurred simultaneously. Data on the amount, time taken, and speed of movements measured at each anatomical landmark showed that the working-side corner of the mouth moved a greater distance at a faster pace and, therefore, in less time than that of the balancing-side corner of the mouth. This is conceivably due to the aforementioned differences in X- and Z-axis movements of the working-side and balancing-side corners of the mouth. Further comparisons and studies with expansion of the subjects to include children will be necessary.