As a basic model of fatigue cracks in composite materials, the fatigue crack growth behavior was studied for the case that a crack grows perpendicularly to the bonded boundary of two dissimilar materials from the material of lower Young's modulus (E1) to that of higher one (E2). A set of fatigue tests were conduced on plate specimens of epoxy-epoxy or epoxy-metal composite. These specimens were selected and prepared for this study to produce a wide range of E2/E1 and to have a fully bonded boundary. The fatigue crack growth rate (da/dn) in the material E1 for the specimens with various E2/E1 ratios was measured and compared with that in the homogeneous material (E1). The stress intensity factor range ΔKre was calculated experimentally from this comparison of da/dn. The data of fatigue crack growth rate were corrected with ΔKre/E1, and the ΔKre/E1-da/dn relation was represented by one straight line for various dissimilar materials including dissimilar metals. From these results, it is confirmed that the fatigue crack growth rate in dissimilar materials depends on K and the present testing method is useful as the simulation test of fatigue crack growth in general dissimilar materials.