A new species of the colubrid genus Dendrelaphis Boulenger, 1890 is described. Dendrelaphis haasi sp. nov. ranges from the Malaysian Peninsula to Sumatra, Java and Borneo. Within this range it also inhabits the islands of Pulau Tioman, Nias, Billiton and the Mentawei Archipelago. D. haasi is similar to Dendrelaphis pictus (Gmelin, 1789) with which it occurs sympatrically. However, univariate and multivariate analyses demonstrate that D. haasi differs from D. pictus in several aspects of its coloration and morphology. D. haasi differs from D. pictus in possessing a faint, instead of bright, ventrolateral line, a narrow, instead of broad, postocular stripe, broader vertebral scales, a lower number of temporal scales, a higher number of subcaudals, a smaller eye, a longer tail and a parietal scale that extends further down the side of the head. The discovery of D. haasi as well as the recent description of D. kopsteini Vogel and Van Rooijen, 2007, both fairly common species, demonstrate that the systematics of Dendrelaphis are still poorly explored and thus need further investigation. An updated key to the Dendrelaphis-species of the Sunda Region is provided.