The mechanical properties of grey cast irons can be modified with alloying elements. Cr and Cu have been known as elements that can improve tensile strength of grey cast irons. The improvement of tensile strength can be influence of fatigue strength. The goal of this research is to study the effect of alloying Cr and Cu on the fatigue strength. Four materials of grey cast irons have been conducted to high cycle fatigue (HCF) testing on the rotating bending machine. The first material is grey cast irons without added Cr and Cu, and the other have added. The percentages of Cr have been added are 0,23% wt, 0,32%wt and 0,47%wt and Cu 0,6%wt to 0,7%wt. The metallography examinations and tensile test also have been conducted. The results of this research are the material has the same microstructure. The microstructures of its materials are pearlitic grey cast irons with graphite type VII, distribution A and size of graphite 3-5. The tensile, endurance and fatigue strength of materials, which added Cr and Cu significantly increasing, compared with base materials. The tensile strength rose from 191MPa to 232MPa and the endurance strength raised from 94 MPa to 110MPa. However three modified materials, which added Cr and Cu has the same effects.