Gabexate mesilate is a non-peptide protease inhibitor, developed in Japan, which is used in the treatment of acute pancreatitis and disseminated intravascular coagulation. This compound is readily hydrolyzed as it has ester bonds in its structure. It is now out of patent in Japan and there are many generic versions on the market. The crystal structure and the hydrolysate content of the branded product and nine generic versions were evaluated by X-ray diffractometry, thermal analysis and HPLC. The results showed that generic products containing mannitol as an additive had a higher content of hydrolysate as an impurity than the branded product or generic products formulated without mannitol, suggesting that the crystal structure might be altered and stability impaired in mannitol-containing drug products.