The refined fish oil was catalyzed and oxidized with air, then sulphited. This two-step process to produce oxidized-sulphited fish oil is an improvement of the traditional one-step process. The merits of this process are: more convenient operation and shorter producing period. The optimized conditions for oxidation are: temperature, 65~70℃; amount of catalyst, 2%; reaction time, 5~6h; and those for sulphitation are: temperature, 70~75℃; amount of sulphite, 8~12%; reaction time, 2~3h. It is shown from application experiments that the oxidized-sulphited fish oil fatliquoring agent produced using this process has remarkable properties.