cis- and trans-Dicyclohexyl-3,3′,4,4′-tetracarboxylic acid and their dianhydrides were prepared from tetramethyl dicyclohexyl-3,3′,4,4′-tetra-carboxylates by hydrolysis and subsequent dehydration. The trans dianhydride 2b was found to be sensitive to temperature. However, once the imide ring is formed in the reaction with an amine, the model compound is thermostable. The products were characterized by 1 H and 13 C NMR, and also by two-dimensional COSY spectroscopy. In the hydrolysis of cis-tetramethyl dicyclohexyl-3,3′,4,4′-tetracarboxylates in steam under high-pressure, trans-dicyclohexyl-3,3′,4,4′-tetracarboxylic acid was formed, while the treatment of cis-dicyclohexyl-3,3′,4,4′-tetracarboxylic acid in steam under high-pressure afforded also trans-dicyclohexyl-3,3′,4,4′-tetracarboxylic acid. In a deuterium tracer experiment of cis-1a, the 3,3′,4,4′-tetradeuterated dicyclohexyl-3,3′,4,4′-tetracarboxylic acid 2a was formed. An isomerization mechanism was postulated from this findings.