Аннотация:We describe a new species of karst-dwelling pitviper from Sa Kaeo Province in eastern Thailand based on morphological and molecular (2,296 bp from cyt b, ND4, and 16S rRNA mitochondrial DNA genes) lines of evidence. Our phylogenetic analysis places the new species as a sister lineage of Trimeresurus venustus (p = 2.7% and 3.7% for cyt b and ND4 genes, respectively). It is also closely related to T. cardamomensis (p = 2.1% and 2.6% for cyt b and ND4 genes, respectively). To date, the new species is known from only two adult specimens, and its distribution seems to be restricted to a narrow limestone karst area in the province of Sa Kaeo in Thailand near the national border with Cambodia. Additional studies are required to understand its life history, distribution, and conservation status. The discovery of this new species brings the total number of known Trimeresurus to 51 species, 19 of which occur in Thailand, including five that are endemic to this country.