Butanetetracarboxylic acid (BTCA) has been used as the most effective nonformaldehyde crosslinking agent for cotton and wood pulp cellulose. Our previous research has indicated that a. polycarboxylic acid esterifies cellulose in two steps : the formation of a five-membered cyclic anhydride intermediate by the dehydration of two adjacent carboxyl groups, and the reaction between cellulose and the anhydride intermediate to form an ester linkage. In this research, we investigated the formation of carboxylic anhydrides by BTCA and other polycarboxylic acids in powder forms, and as finishes applied to cotton fabric using thermal gravimetry, differential scanning calorimetry, and Fourier transform infrared spectroscopy We found that BTCA and other polycarboxylic acids in powder forms start to form five-membered cyclic carboxylic anhydrides when the temperature reaches the vicinity of their melting points. The formation of carboxylic anhydride is accelerated above the melting points. We also found that BTCA forms anhydridies at lower temperatures when it is applied to cotton fabric as a finish. An increase in temperature increases both the amount of anhydride and the amount of ester formed on the cotton fabric.