The natricine snake genus Smithophis Giri, Gower, Das, Lalremsanga, Lalronunga, Captain, and Deepak, 2019, is represented by four species, three of which are distributed in northeast India and Bangladesh, and a single species in Yunnan and Myanmar. In the past, S. bicolor (Blyth, 1855) was said to be widespread across northeast India and Myanmar; however, recent studies have shown it to be a species complex. Here, we describe a new species of the complex from the Indian state of Mizoram that resembles S. bicolor. The new species differs in bearing a patterned dorsum, a darker venter, and moderately keeled sacral scales. Re-examination of types of S. arunachalensis Das, Deepak, Captain, Wade, and Gower, 2020, shows the presence of strongly keeled sacral keels in males, which is an important diagnostic character. A revised key to members of the genus is presented with notes on S. arunachalensis.