Vocal communication on the proboscis monkey (Nasalis larvatus) was poorly documented. d. The objectives of the research were to phonetically identify vocalizations of this monkey, measure their duration, and interpret their functions. Six vocalizations, along with eleven behaviors were found. Duration of four vocalizations ranged 0,36-1,30 sec and of two-vocalizations was supposed to be less than 0,25 sec. Vocalizations function to reflect the state of angry, happy, or dissapointed, show the domination an individual to others, and warn the group.