Abstract: The organic substances were analyzed during fermentation of sesame seed cake, soybean cake, peanut seed cake and rape seed cake under constant temperature and humidity conditions. The results showed that large amount of higher fatty acid, organic acid and amino acid were produced during the fermentation of four kinds of plant oil cakes, but the quantity was different owing to the different chemical composition of oil cakes. The C16 and C18 acids were the dominant component in the higher fatty acids produced during fermentation, and the content of saturated acids was higher than that of the unsaturated acids obviously. In the produced organic acids, the contents of lactic acid, malic acid, citric acid, succinic acid, tartaric acid and acetic acid were higher than oxalic acid. The content of organic acids and higher fatty acids were increased with fermentation time, and they reached the highest value in specified fermentation stage. However, the glutamate occupies first place, aspartate, leucine and arginine comes second in all amino acids produced during the fermentation of oil cakes. The content of amino acids are significantly decreased after seventy days of fermentation. Among the four plant oil cakes, soybean and peanut cake produced most amino acids during fermentation, but the sesame seed cake showed the fastest fermentation rate, and the rape seed cake expressed the slowest.