Water-extractable dicarboxylic acids (C₃–C₉) were detected in sediments of a stratigraphic sequence from Miocene to Pliocene in the Shinjo basin, Japan. Contents of these acids in the sediments ranged from 0.01 to 10 n mol g^–1, showing generally succinic acid the most abundant of all. The saturated normal dicarboxylic acids generally showed a decrease in contents with an increase of carbon numbers in their molecular distribution patterns. Unsaturated acids exhibited strong predominance of cis isomer over trans one with the C₄ and C₅ acids in the lower part of the sequence. Optical isomers of branched dicarboxylic acids, especially, methylsuccinic acid and 2-methylglutaric acid were present in racemic mixtures in the lower part of the sequence. The depth profile of the contents of the saturated normal dicarboxylic acids as well as their molecular distribution patterns was different from that of monocarboxylic acids (C₃–C₉) in the same sediments (Shimoyama et al., 1991), suggesting different chemical forms of the two kinds of the carboxylic acids in the sediments.