We compared the morphological characters of populations of the Caucasian Pit Viper, Gloydius halys caucasicus, from different regions of the Alborz mountain range. For this purpose, we studied 7 metric and 21 meristic characters in 12 specimens from the western Alborz, 44 specimens from the eastern Alborz and nine specimens from the central Alborz Mountains. The results of the statistical analyses by npMANOVA, ANOVA and Kruskal Wallis tests showed significant differences between all three populations, while the western Alborz and the eastern Alborz populations are more distinct from each other. The important characters showing differences between them are: Subcaudals, dorsal scales in anterior part, dorsal scales in posterior part, supralabial scales, scales between gulars, gulars, ventrals, ratio of snout length over snout width, and ratio of snout length over head length.