<p>This study investigated the kinematics of mandibular movements during mastication in Japanese macaques (Macaca fuscata) using a non-invasive approach. Traditional methods involved the use of mandibular kinesiography developed for humans, which is difficult to adapt to primate subjects. Additionally, studies involving primates using novel optical motion capture technology required surgical implantation of bone screws to accurately analyze mandibular movements, presenting challenges in terms of invasiveness and technical precision. The authors propose a technique using optical motion capture technology and paint markers on the skin to quantify lateral movements during mastication; this approach minimizes invasiveness by eliminating the need for screw implantation in bone. Three male macaques with various stages of permanent dentitions were studied, and their mandibular movements were recorded during mastication of three different food types: apple pieces, radish pieces, and solid monkey chow. The trajectories of mandibular movements were analyzed, focusing on the mediolateral range of motion (RoM) and the frequency of mouth movements. Results indicated variations in lateral movements with different food types, with solid monkey chow inducing the highest mediolateral RoM. This method offers insights into primate masticatory behavior, providing a less invasive alternative for future studies on non-human primates. The study emphasizes the importance of considering the further investigation into the physical properties of test foods and the accuracy of the methodology.</p>