Flavin-containing monooxygenase 2 (FMO2), also known as dimethylaniline monooxygenase [N-oxide-forming] 2, is a mammalian enzyme that in humans is encoded by the FMO2 gene. The gene is found in a cluster with the FMO1, FMO3, and FMO4 genes on chromosome 1.

FMO2 is a member of the family of flavin-containing monooxygenases, NADPH-dependent enzymes that catalyze the oxidation of many drugs and xenobiotics. It catalyzes the N-oxidation of some primary alkylamines through an N-hydroxylamine intermediate.

In humans, FMO2 is expressed in lung tissue. The most common isoform, FMO2*2A, contains a premature stop codon, leading to a truncated protein with no catalytic activity that is probably rapidly degraded. The other isoform, FMO2*1, present in sub-Saharan Africans (up to 50%), African-Americans (26%) and Hispanics (2–7%), is functional. Its substrates include thioether-containing pesticides, the anti-tuberculosis drug ethionamide, as well as α-naphthylthiourea and other thioureas.