In the crystal structure of the title compound, (NH(4))[AsO(2)(OH)(C(6)H(4)NO(2))], the 4-nitrophenylarsonate anions and ammonium cations are linked through hydrogen bonds to form infinite chains along the b axis. The hydroxyl O atom of the 4-nitrophenylarsonate anion acts as both an acceptor and a donor of hydrogen bonds. All atoms are located in general positions.