Brassica nigra plants showing symptoms caused by root-knot nematodes were detected in the municipality of La Joya, Arequipa Province, Peru. Based on morphology, esterase phenotypes, and species-specific characterized amplified region (SCAR) sequence, the causal agent was identified as Meloidogyne incognita. Pathogenicity was confirmed by a modified version of Koch’s postulates. To our knowledge, this is the first report of M. incognita infecting Brassica nigra in Peru.