Opisthotropis jacobi, also known commonly as the Chapa mountain keelback, Jacob's mountain stream keelback, and Jacob's stream snake, is a species of snake in the subfamily Natricinae of the family Colubridae. The species is native to Vietnam and China.
The specific name, jacobi, is in honor of German entomologist Arnold F. V. Jacobi.
O. jacobi is found in extreme northern Vietnam and in adjacent Yunnan Province, China.
The preferred natural habitats of O. jacobi are forest and streams, at altitudes of .
O. jacobi may attain a total length (including tail) of . Dorsally, it is uniformly shiny black. Ventrally, it is also shiny black but with light-edged ventrals and subcaudals. The dorsal scales are smooth, and arranged in 15 rows throughout the length of the body.
O. jacobi preys upon earthworms, freshwater shrimp, fishes, and frogs and their tadpoles.
O. jacobi is oviparous.