The one bath wet-fixation finish of the cotton fabrics was studied by the use of mixed acid as a catalyst. The degree of degradation of the cotton fabrics treated with acid was evaluated by the measurement of molecular weight and breaking strength. N-dodecyl mercaptan, as a model compound of cellulose, was reacted with dimethylol dihydrowxy ethylene urea (DMDHEU), and the reactivity at various conditions was investigated. As a catalyst for the one bath wet-fixation finish, the mixture of formic acid and other acid (e.g. lactic acid)was better than formic acid alone in physical properties of finished cotton fabrics.