The title molecule, N-diphenylphosphino-4-methylpiperidine selenide(1), was prepared and characterized by elemental analysis, H-1-NMR, P-31-{H-1} NMR, IR, and X-ray single-crystal determination. The compound crystallizes in the monoclinic space group P 2(1)/c. In addition to the molecular geometry from X-ray determination, vibrational frequencies and gauge, including atomic orbital (GIAO) H-1- and P-31-{H-1} NMR chemical shift values of the title compound (1) in the ground state, were calculated using the Hartree-Fock and density functional methods with the 6-31G(d, p) basis set. The calculated results show that the optimized geometries can well reproduce the crystal structures. Besides, the theoretical vibrational frequencies and chemical shift values show good agreement with experimental values. The predicted nonlinear optical (NLO) properties of the title compound are greater than those of urea. In addition, density functional theory (DFT) calculations of the molecular electrostatic potentials (MEPs), frontier molecular orbitals (FMOs) of the title compound were carried out at the B3LYP/6-31G(d) level of theory.