The second-order nonlinear optical (NLO) properties of various Pt(II) acetylcetonate complexes bearing a substituted cyclometalated 4-styryl-2-phenylpyridine (ppy-4-styryl-R, with R = NEt 2 , OMe, H, NO 2) were investigated in DMF solution on working with an incident wavelength of 1907 nm by the EFISH technique, whereas the dipole moments were determined by density functional theory (DFT) calculations. In addition, a Pt(II) complex with the ppy-4-styryl-NEt 2 ligand, which was the most NLO efficient chromophore due to a particularly high dipole moment, was dispersed in a polymethylmethacrylate matrix and then oriented by poling to give a composite film characterized by a good and quite stable second harmonic generation (SHG) signal.