A process for removing nitrogen oxides from exhaust gases containing at least nitrogen oxides and volatile metal compounds by the use of a catalyst having prevented activity reduction due to the volatile metal compounds and having a superior durability is provided, which process comprises contacting the exhaust gases with a catalyst containing TiO.sub.2, a compound active to nitrogen oxides-removing reaction such as oxides of V, Cr, Mo, W, Fe, Co, Ni, Cu, Ce, etc. and/or sulfates thereof and a metal sulfate containing water of crystallization such as those of Al, Mg or Mn, in the presence of ammonia at 150.degree. to 600.degree. C.