The method provides nitro compounds at a high conversion and selectivity by nitrating substrates under comparatively mild conditions in the absence of catalysts. Organic substrates are nitrated using no catalysts or ozone, but using (1) at least one nitrogen compound selected from N.sub.2 O or NO and oxygen. It is advantageous for the nitration reaction to employ a nitrogen compound obtained by a reaction of the nitrogen compound with oxygen, particularly a nitrogen oxide comprising N.sub.2 O.sub.3 as a main component. Additionally, organic substrates are nitrated using (2) NO.sub.2. The substrates include a compound having a methine-carbon atom, and a compound having a methyl group or methylene group in an adjacent position to an aromatic ring.