A desulfurization process which comprises the steps of bringing a combustion exhaust gas into contact with a gypsum slurry containing 1% or less of calcium carbonate in a first absorption tower, and then bringing the combustion exhaust gas into contact with a gypsum slurry containing 1% or more of calcium carbonate in a second absorption tower. SO.sub.x can be removed from a combustion exhaust gas with a high efficiency in accordance with a wet lime/gypsum method.