The complete genome sequence of a wild tomato mosaic virus (WTMV) isolate (named WTMV-Sn) was determined and identified in Solanum nigrum in China. The complete genome of WTMV-Sn is 9,659 nucleotides in length, excluding the poly(A) tail and encodes a polyprotein of 3,074 amino acids. This is the first report of WTMV infecting S. nigrum. Despite the high degree of sequence similarity between the WTMV-Sn and WTMV-XC-1 isolates, the 349 nucleotides at the 5' terminus of WTMV-Sn appear to have originated by recombination with another isolate. The recombination parent remains unknown, but the recombination region shares 74.57% sequence identity with isolate WTMV-Laichau, which is below the species demarcation threshold for the genus Potyvirus. A pathogenicity test showed that WTMV-Sn can infect tobacco. This suggests that variation in the P1 cistron of WTMV-Sn may contribute to its ability to infect S. nigrum.