<p>Movement and behavioral patterns of a species reflect its response and adaptation to the environment. These responses form diel activity patterns that can be further categorized into certain temporal niches, namely, diurnal, nocturnal, crepuscular, and cathemeral. The diel activity pattern of Japanese serow (<i>Capricornis crispus</i>) has mostly been studied using camera traps and direct observations, which might have introduced bias, particularly with nocturnal activities. This study aimed to investigate the diel activity pattern of Japanese serow and seasonal changes in it using built-in triaxis activity sensor GPS collars. This study was conducted in Tokyo, central Japan, with data collected from five individuals. Results showed significantly higher activity during day than that during night across all individuals. The absence of natural predators, such as the Japanese wolf (<i>Canis lupus hodophylax</i>), and direct human threats, like hunting, suggests limited selective pressure for regular activity pattern modification. Seasonally, activity peaked in spring and autumn. In spring, these peaks may be attributed to increased foraging for crude protein from shoot sprouts after colder months. In autumn (September to November), the peak in activity level may be attributed to mating behavior. Therefore, classification of behaviors using activity sensors can provide a better understanding of variations in activity level between sexes and at the population level. This study is the first to use activity sensors to understand the diel and seasonal activity patterns of Japanese serow, reflecting its novelty and effectiveness.</p>