Due to the fact that magnetic properties of ferromagnetic materials are highly microstructure sensitive, magnetic non-destructive testing (NDT) techniques for material evaluation have developed very quickly in recent years. This dissertation is mainly focused on the magnetic hysteresis measurement technique. The modelling of structure-sensitive magnetic properties will be discussed first. As a result, the relationship between defect density, the initial permeability and the hysteresis parameter k will be developed. This is followed by the application of magnetic hysteresis measurement techniques in the detection of fatigue damage and creep damage. It will be shown that structure sensitive magnetic properties such as coercivity, remanence, hysteresis loss and initial permeability are very sensitive to material degradation due to fatigue and creep effects. Finally, practical problems in hysteresis measurement will be discussed and techniques to overcome these difficulties will also be presented.