Under fully reversed and pulsating load, the low cycle fatigue tests of notched composite weldment plates were carried out and the plates were composed of high strength steel HT60 and mild steel SM 41, and symmetrically arranged about the axis parallel to the direction of axial load. Strain behavior near a notch root was analyzed by Moire method at the successive stages of cyclic loading and static strain distribution near a notch root was calculated by FEM. These strains and their distribution were used to the formulae for the estimation of crack initiation life proposed by the authors. From these test results and analysis, it was found that the fatigue crack initiation life of the notched composite weldment specimen was equal to the notched single material one when the strain behavior near the notch root was equal, but crack propagation life of the composite specimen was generally different from that of the single material one and was dependent on the arrangement of materials.