The Tam Dao Mountain Stream Keelback, Opisthotropis tamdaoensis Ziegler, David & Vu, 2008, was previously described, based on one single holotype and subsequently expanded according to four newly-collected specimens from the type locality. Information on this species is extremely limited.

On the basis of newly-collected Opisthotropis specimens from Hekou, Yunnan, China, this study reports the first country record of Opisthotropis tamdaoensis from China. The Chinese Opisthotropis tamdaoensis population totally agrees with the original description of this species and revealed only a minor genetic distance (lower than 2.9%) in the mitochondrial gene fragment of the cytochrome b (Cytb) compared with the topotypic population. Based upon the our newly-collected specimens and published data, we revised the diagnosis of Opisthotropis tamdaoensis:

nasal not divided below nostril;loreal usually 1, not in contact with internasals;pre-oculars 1–2, postoculars 2 subocular, usually 1;anterior temporals 1–2, posterior temporals 2–4;supralabials usually 9, only the fifth or fifth to sixth supralabial (rarely none) in contact with the orbit;infralabials usually 9–10;first pair of chin shields longer than the second pair;dorsal scales smooth anteriorly, keeled posteriorly, in (17–19)-17-17 rows;tails relatively short, TaL/TL 0.143–0.161;pre ventrals 0–4, ventrals 160–176, precloacal divided; 48–56 divided subcaudals;uniform olive-grey dorsum, with a dark longitudinal lateral stripe within the dark flank colouration, ventral side pale or light yellow, without sharp transition towards the dark dorsal colouration, subcaudal region may bear dark mottling.

This finding broadly extends our understanding of this poorly-known snake species and raises the total known Opisthotropis number in China to 14. Moreover, this study reports the second Opisthotropis species in Yunnan Province, China.