Nonlinear optical organic materials of N,N-diphenylbenzamide (NNDPB) and 4-fluoro-N,N-diphenylbenzamide (FNNDPB) are synthesized from benzoylation of N,N-diphenylamine using the substituted benzoyl chlorides. The single crystals of NNDPB and FNNDPB are grown by a slow evaporation technique. Single-crystal X-ray diffraction shows that both the crystals belong to orthorhombic crystallographic system with space group Pbca. Fourier transform infrared spectrum shows the chemical bonding and various functional groups, the carbonyl peak appeared at 1647 and 1651 cm −1 in NNDPB and FNNDPB compounds, respectively. 1 H and 13 C nuclear magnetic resonance analysis examines the placement of aromatic protons and carbons are identified to the synthesized materials. UV-vis near IR spectra analysis showed 100% transmission in the visible region for both NNDPB and FNNDPB crystals. As-grown crystal dielectric constant and dielectric loss are inversely proportional to the frequency at all the temperatures. The thermal properties of NNDPB and FNNDPB crystals are studied from thermogravimetric analysis/differential thermal analysis analysis, it is thermally stable up to 483 and 503 K. Crystal growth mechanism and defects are observed from etching studies. The relative second harmonic generation efficiency is measured by Kurtz-Perry powder technique and is found to be 1.55 and 1.7 times as that of potassium dihydrogen phosphate.