Condensation of 3, 5-dinitrobenzoic acid and methyl ketones, such as acetone and acetophenone, was carried out in the presence of alkali and a condensate was obtained as blackish purple crystalline powder. Acidification of these condensates effected decomposition into each component, while oxidation with hydrogen peroxide in acetic acid solution afforded a substance which colors reddish violet to alkali. These were considered to be compounds formed by introduction of acetonyl or phenacyl group into the ring. Condensation of 2- or 4-acetonyl- and 2- or 4-phenacyl compounds with ethyl 2- or 4-chloro-3, 5-dinitrobenzoate and ethyl acetoacetate and ethyl benzoyl-acetate was carried out. Ketonic decomposition of the condensates so obtained effected concurrent saponification, and 3-methyl- and 3-phenyl-5, 7-dinitroisocoumarin, m. p. 104° and m. p. 211°, and 4-acetonyl- and 4-phenacyl-3, 5-dinitrobenzoic acid, m. p. 196° and m. p. 202°, were obtained. The oxidation products of the blackish purple condensates were identical with 3-methyl- and 3-phenyl-5, 7-dinitroisocoumarin, and this fact proved that the condensation took place at the position 2 to the carboxyl group.The condensation of 2- or 4-chloro-3, 5-dinitrobenzoic acid and acetone, and acidification of the condensate so obtained afforded 3-methyl-5, 7-dinitro-8-chloroisocoumarin as the chief component and a small amount of 3-methyl-6, 7-dinitro-6-chloroisocoumarin from the 2-chloro derivative. It was concluded that in this case also, as in the case of the foregoing 3, 5-dinitrobenzoic acid, the condensation took place at the position 2 to the carboxyl group.