Wet precipitation (rain and snow) and aerosol samples were collected in Tokyo and analyzed for dicarboxylic acids (C₂-C₁₁), ω-oxocarboxylic acids (ωC₂-ωC₆), pyruvic acid and α-dicarbonyls (glyoxal and methylglyoxal) using a capillary GC and GC/MS. Molecular composition of dicarboxylic acids and related polar compounds in both wet precipctation and aerosol samples showed a strong seasonal trend. In the winter wet precipitation samples, longer chain dicarboxylic acids (C₆-C₉), unsaturated diacids and ketocarboxylic acids which are thought as intermediates of photochemical reactions were found to be relatively more abundant than the early summer samples. By contrast, oxalic acid (C₂) which has been proposed as an end product of photochemical chain reactions of anthropogenic and biogenic organic compounds was found to be more enriched in the early summer precipitations, suggesting that oxalic acid is more abundantly produced in the middle and upper troposphere. Similar seasonal trend was also found in the aerosol samples. This study suggested that the atmospheric photochemical reactions which are more active in early summer than in winter are imprinted in the molecular composition of dicarboxylic acids and related polar compounds in the wet precipitation and aerosol samples.