The invention provides a nonlinear optical material comprising a compound represented by the general formula (1): ##STR1## wherein R.sup.1 denotes an electron attractive group, R.sup.2 denotes a group selected from the group consisting of a hydrogen atom, methyl group, methoxy group and electron attractive group, R.sup.3 denotes a straight-chain alkylene group, and X denotes an oxygen or sulfur atom. The invention also relates to a method of manufacturing a nonlinear optical material comprising the steps of dissolving a compound represented by the general formula (1) in an organic solvent, and evaporating the solvent while keeping its temperature constant or lowering its temperature, thereby growing a crystal of the compound represented by the general formula (1). The nonlinear optical material of the invention possessing a molecular structure realized by linking structures having a strong electron attractive group and weak electron donative portion with straight-chain alkylene portions, and thus a nonlinear optical material having a shortened absorption edge wavelength and excellent crystallinity may be obtained. These nonlinear optical materials can be effectively utilized as the nonlinear optical material for an optical wavelength converter.