Since a standard spot welding condition sets target of diameter of nugget to 5√𝑡, the effect of nugget diameter on fatigue strength was included into the S-N curves of spot-welded joints with various sheet thickness. By analyzing the sensitivity of the tensile shear joints and the shear torsion joints with the nugget diameter 5√𝑡, the effects of sheet thickness and nugget diameter on fatigue strength were 7 to 3 for tensile shear and about 4 to 6 for shear torsion. The analyzed results for tensile shear agreed well with the fatigue test results.