In the title compound, C(25)H(22)N(2)OSe, the fused six-membered cyclo-hexene ring of the 4,5,6,7-tetra-hydro-1,2,3-benzoselenadiazole group adopts a near half-chair conformation and the five-membered 1,2,3-selenadiazole ring is essentially planar (r.m.s. deviation = 0.004 Å). There are weak inter-molecular C-H⋯O and C-H⋯π inter-actions in the crystal structure. Inter-molecular π-π stacking is also observed between the naphthyl units, with a centroid-centroid distance of 3.529 (15) Å.