Nitration of 2-anilinopyridine (II) with a mixed acid afforded 2-(2-nitroanilino)pyridine (III), 2-(4'-nitroanilino)pyridine (V), and 2-(2', 4'-dinitroanilino)pyridine (VI), in a poor yield, but that with excess nitric acid gave VI alone in a high yield. Nitration of II with acetyl nitrate gave VI, 2-(2', 4'-dinitroanilino)-5-nitropyridine (IX), and 2-(2', 4'-dinitroanilino)-3, 5-dinitropyridine (X). II showed different reactivity in nitration with a strong acidic medium and a mild medium like nitric acid in acetic anhydride. In order to elucidate the reactivity of II in each case, it was assumed that II takes an anilinopyridinium ion form in a strongly acidic medium and a neutral anilinopyridine form in the mild acidic medium.