The catalytic activity and stability for steam reforming of CH4 was studied on Ni/Mg-Al prepared by the solid phase crystallization (spc-) method. spc-Ni/Mg-Al showed higher activity than those prepared by the conventional impregnation method such as Ni/MgO or Ni/Al2O3. This catalyst also showed high stability even under a low steam to carbon ratio. The high and stable activity of spc-Ni/Mg-Al is caused by the formation of highly dispersed and stable Ni metals.