The thesis describes the effects of the magnetic field in rolling contact tests of steel by using a two-disc machine and the investigation of its mechanism from contact stress analysis by using FEM and the agnetisation of a ferromagnetic substance. In the tests, two contact kinematic conditions, that is pure rolling and 10% rolling with sliding together with 1.1 and OAT [Tesla] of horizontal static magnetic fields created by permanent magnets were pplied. The results of optical and scanning electron microscopy observations show that finer wear particles and smoother worn surfaces are produced in the presence of the magnetic field. For the generation of the finer wear particles, it is considered necessary that the subsurface crack initiation point is moved towards the surface due to the magnetic field. Wear amounts of the discs are lowered III the magnetic fields under the pure rolling conditions. However, at 100/0 rolling with sliding, the wear amounts are increased in the magnetic fields even though finer particles and smoother surfaces are observed. Both tendencies are unified by calculating the number of cycles required to generate wear particles, which are reduced due to the magnetic field's presence. For these mechanisms, it is considered that domain walls near the contact region are caught by dislocations when the specimen is agnetised and part of the energy for magnetisation activates the dislocation movement resulting in crack initiation.