The organic nonlinear optical crystal 4-nitro-4'-methyl benzylidene aniline (NMBA) having three-dimensional octahedral shape were grown from solutions with polar solvents by slow cooling method with one-dimensional needle-shaped seed crystals. X-ray powder diffraction study made on the grown crystals showed that they belong to monoclinic system with space group Pc. The grown crystals were characterized by different instrumental methods such as differential thermal analysis (DTA) and thermogravimetry (TG), infrared (IR) and nuclear magnetic resonance (NMR) spectral analyses and optical transmittance study. DTA and TG analysis ascertained purity of the synthesized, purified and grown NMBA material. IR spectral analysis reveals different functional groups present in the NMBA molecule. NMR spectral analysis examines different positions of hydrogen atoms in different chemical environments in the NMBA molecule. Optical transmission spectrum gives the optical transmission window of NMBA in the UV-Visible-Near IR region. (C) 2002 Elsevier Science B.V. All rights reserved.