Because of the importance of the surface magnetic properties for the optimal operation of magnetic sensors based on giant magneto-impedance effect (GMI), for the last few years we have studied the surface magnetization reversal and surface domain structure of glass-coated microwires using the magneto-optical Kerr effect (MOKE) technique [1]. Taking into account that the Curie temperature of Co-based microwires lies in the temperature range of approximately 100–450°C (depending on chemical composition), the surface magnetic structure should experience great transformation in a temperature range higher than room temperature. Moreover internal stresses induced by glass coating are the characteristic feature of glass-coated microwires [2]. Obviously the strength of internal stresses depends on temperature. Therefore now we direct our efforts to a new area of the investigation that is very important for the stable operation of magnetic sensors that use microwires as active elements — the influence of changing temperature on the surface magnetic structure.