<p>Vigilance behavior serves as a critical adaptation for detecting predators and monitoring conspecifics. We investigated factors influencing vigilance patterns, measured as scanning behavior, in male and female golden snub-nosed monkeys (<i>Rhinopithecus roxellana</i>) using 1089 5-min focal samples from a free-ranging, habituated group of 30 adults (6 adult males and 24 adult females) at Dalongtan, Shennongjia National Park, central China, during February-July and September-November 2022. Females exhibited high scanning levels in open habitat, when positioned farther from social partners, in smaller one-male, multifemale units (OMUs), and when they had vulnerable infants (infants under 6 months of age). Scanning was also positively correlated with relatedness among OMU members. Females exhibited the least scanning behavior during feeding. In contrast to females, males showed significantly higher levels of scanning, which increased with OMU size and distance from the OMU but exhibited no significant variation among habitats or activity states. Males primarily directed scanning toward rival males and females from other OMUs, suggesting a mate defense function. These results show distinct sex-specific functions of scanning behavior: females prioritize antipredator and infant protection strategies, while males focus on social vigilance and mate defense. Our findings highlight the interplay of ecological and social factors in shaping scanning behavior and the importance of considering sex differences in studies of primate behavior.</p>