Brass is a popular engineering material used in a variety of applications requiring good strength, ductility, corrosion resistance and machinability. This work focuses on the analysis of Stress – Strain Hysteresis Loops obtained in low cycle fatigue experiments in order to determine the internal and effective components of the stress amplitude which provide valuable information about damage mechanisms. Cyclic plastic straining has been studied using the SAP method (Statistical Approach of Plastic deformation). This approach allows the evaluation of the effective and internal stresses, effective elastic modulus and the probability density function, f(σic), which reflects the microstructure of the plastically deformed material. f(σic) obtained from each reversal exhibits two peaks in α/β brass, corresponding to the plastic deformation of each component phase of this material. At low strain amplitudes and during the initial loading cycles, a single peak has been generally observed. However, at high strain amplitudes and at the stabilization stage of the hysteresis loop, two distinct peaks could be distinguished. Further, relative to the effective stress, the internal stress shows a hardening effect with strain amplitude.