In this study, the wear behaviour of GGG40 materials, which are widely used in manufacturing of gears, was investigated by considering slip-ratio of the disc specimens so that working conditions of gears are simulated. The variations in surface profiles, weight, frictional force and surface quality were observed for evaluation of wear behaviour of the nodular cast iron specimens. It is indicated that the surface roughness value (Ra) increased after the test conducted at different loading and slip-ratios. It is understood that graphite debris appeared on the specimen surface are adhered by the frictional forces to the frictional pair surfaces and lead to easier friction relatively between disc surfaces due to their lubrication effects. Therefore, the surface roughness of the discs is not only increased by the graphite layer, but it is also increased by relatively lower wear. In accordance to this, as the test load is increased, mass losses of the specimens gradually increased while they decreased by slip-ratios. The main cause of this situation is graphite adhering to the frictional surface. As it is expected, the frictional forces recorded during the wear tests sharply increased during the running-in period of friction and then they became nearly constant during the steady-state period. The wear mechanism of the friction applied under these test condition is predominantly adhesion due to the graphite layer occurred on the surfaces of tribocouple.