Grey cast iron is traditionally characterised by its tensile strength. Procedures to increase the fatigue limit were therefore assumed at increasing the tensile strength. In contrast in the present work the stress/strain behaviour and the area of the fatigue limit on the stress/strain curve was investigated by high resolution stress/strain measurements. Furthermore the influence of microstructure (eutectic cells size, amount of ferrit, length of lamellae, frequency of particles) on the stress/strain curve and on the fatigue limit (r=-1) was investigated. The assumption of this procedure is that different parameters on the tensile strength and fatigue limit affect each other similarly but in different strength. This was shown in high resolution tensile strength measurements using strain gauges. Thereby comprehensive database for grey cast iron including tensile strength, hardness, tangent and secant modulus, microstructure parameters, chemical composition and fatigue limits was established. Moreover an improved method for a better estimation of the fatigue limit from tensile test measurements obtained by strain gauges was developed.