The Schiff base compound, N-N'-bis(4-methoxybenzylidene)ethylenediamine (C18H2ON2O2) has been synthesized and its crystal structure has been investigated by X-ray analysis and PM3 method. The compound crystallizes in monoclinic space group P2(1)/n with a = 10.190(1), b = 7.954(1), c = 10.636(1) Angstrom, beta = 111.68(1)degrees, V = 801.1(1) Angstrom (3), Z = 2 and D-cal = 1.229 Mg m(-3). The title structure was solved by direct methods and refined to R = 0.056 for 2414 reflections [I > 3.0 sigma (I)] by full-matrix anisotropic least-squares methods. The energy profile of the compound was calculated by PM3 method as a function of theta [N1'-C9-C9-N1]. The most stable molecular structure of the title compound is the anti conformation, which is different in energy by 5.0 and 1.0 kcal mol(-1) from the eclipsed conformation I and gauche conformations, (IH and V), respectively. (C) 2001 Elsevier Science B.V. All rights reserved.