合趾猿（学名：Symphalangus syndactylus）或大长臂猿是灵长目动物，为长臂猿当中体型最大的一种。合趾猿是其他长臂猿的大小的两倍，达到1米的高度，重达14公斤。

合趾猿分布于东南亚的马来西亚及苏门答腊，栖身于热带雨林以及高山森林。

The siamang (Symphalangus syndactylus) is an arboreal black-furred gibbon native to the forests of Malaysia, Thailand, and Sumatra. The largest of the gibbons, the siamang can be twice the size of other gibbons, reaching 1 m in height, and weighing up to 14 kg. The siamang is the only species in the genus Symphalangus.