In this work the magnetic anisotropy of the 15Mo3 type steel was investigated which was induced by deterioration process caused by thermal shock fatigue. The applied thermal shock fatigue investigation can model the material degradation due to long term service in high temperature environment. The 15Mo3 steel is widely used as reheating pipeline base material of power plant boilers. Magnetisation curves were measured to characterise the induced magnetic anisotropy due to thermal shock fatigue process. A parallel motion vibrating sample magnetometer (PMVSM) which was designed at the Department of Materials Science and Engineering of BUTE was used for the magnetic measurements.