The change of strength and water vapour diffusion resistant by soluble salts was investigated in the tuff and granite used in many stone monuments of Gyeongju area. With Na2SO4 and CaSO4 ․ 2H2O were treated the rock samples to understand the difference of solubility. The densities of the tested rocks were increased by the impregnation of CaSO4 ․ 2H2O and Na2SO4. The flexural strength was increased in the tuff samples but decreased in the granite as the salts increased in the pore. In the tuff, the uniaxial compressive strength was increased by CaSO4 ․ 2H2O, but decreased by Na2SO4. In the granite, it was decreased slightly by CaSO4 ․ 2H2O, but increased by Na2SO4. The water vapour diffusion resistant was increased by the salts in both rocks. As results, it was cleared that the mechanical strength colud be increased in early stage of weathering by the accumulation of salt and water vapour diffusion resistant.