Behaviors exhibited by prey species towards predators (including humans) can reduce feeding time and increase time spent in vigilance, thereby impacting animal condition and ultimately limit populations, even when actual mortality from predation is low. Here, we test whether behavioral profiles in an endangered ape, Javan gibbons (Hylobates moloch), correspond to varying degrees of human disturbance in a human-impacted sacred forest, Cagar Alam Leuweung Sancang, West Java. Data were collected August 2010–July 2011. Although all groups reacted differently to human presence, overall, gibbons responded by reducing time spent on conspicuous behavior (e.g., vocalizing, feeding, traveling, and social interactions) as the number of humans in the area increased or distance to the nearest human decreased. In addition, gibbon responses to encountering humans were also more like their responses to encountering potential predators than they were to encountering monkeys or other gibbons. These results support the hypothesis that as human presence and encounter rates increase, gibbons alter their behavior in ways consistent with anti-predator behaviors. Assessing how this endangered species responds to human presence is a vital part of their ultimate conservation.