Abstract: An impurity usually present in gossypol prepared from dianilihogossypol was studied and identified as monoanilinogossypol. It was an unreported compound in the literature. By analytical data it is in agreement with the formula C₃₆H₃₅O₇N, and decomposed at 272～275℃. Absorption maxima were observed at wavelengths 439～440, 311, 278, 288 and 245 nm, shoulder peaks at 464 and 390 nm. The extinction coefficient at 440 nm E_1cm^1%(CHCl₃) is 329±6, about (1/2) that of dianilinogossypol. The IR exhibit two strong absorptions at 1610cm^-1 (-CHO)and 1590 cm^-1 (C=N). On MS m/e 593 (M⁺) is recorded. The NMR (in CDCl₃) shows the important signals: δ 11.17 (s, lH, -CHO) and δ 10.13 (d, lH, -HC=N-). The Rf value of monoanilinogossypol on TLC(silica gel-starch, solvent: benzene-chloroform-ethylacetate 40:10:3) is higher than that of gossypol and lower than that of dianilinogossypol. The pure product was pale yellow crystals. The analytical data of synthetic sample are also in agreement with above.The presence of monoanilinogossypol in gossypol interferes with the determination of the latter. Thus, it is necessary to identify the impurity with thin layer chromatography before hand.