In the title compound, C(18)H(14)NSe(+)·HSO(4) (-), the cyclo-pentene ring in the cation has an envelope conformation while the central six-membered 1,4-selenazine ring adopts a sofa conformation. The dihedral angle between the planes of the terminal benzene rings is 68.08 (11)°. In the crystal, the anions form chains along the c axis through O-H⋯O hydrogen bonds. Weak C-H⋯O and C-H⋯π hydrogen bonds, as well as attractive Se⋯Se [3.5608 (8) Å] inter-actions, further consolidate the crystal structure.