Oh heating isatin with aromatic monocarboxylic acids having .alpha.-hydrogen atoms such as p-nitrophenylacetic acid, p-methoxyphenyl acetic acid and .alpha.-naphthylacetic acid in the presence of anhydrous sodium acetate functioning as a catalyst, p-nitrobenzylidene-3-oxindole, p-methoxybenzylidene-3-oxindole and ${alpha}$-naphthobenzylidene-3-oxindole are obtained, respectively. The results of these experiments show that isatin may be used as the carbonyl component in the condensation reaction.