In recent years, powder metallurgy technology has become increasingly popular, because it enables lower production costs and higher material utilization compared to classical metallurgy. One of the frequently used materials in powder metallurgy is sintered steel. It is obtained by the sintering process, where the powder material is pressed into the final shape via mold, followed by heat treatment. During the process, pores appear in the core of the material. That results in lower material density compared to steel obtained by classical metallurgy. The surface layer is usually densified to achieve better mechanical properties of components made of sintered steel subjected to fatigue due to sliding-rolling contact. In order to describe the constitutive behaviour of densified sintered steel components by numerical simulations, it is necessary to model the variable material properties depending on the density. This thesis considers the sintered steel Astaloy Mo+0,2C with a density of 6,5 g/cm3, whose surface layer has been densified to a density of 7,5 g/cm3. Two depths of the densified layer were taken into consideration: 0,5 mm and 1 mm. In this paper: 1. Dependence of constitutive behaviour parameters of sintered steel on material density was determined based on the results of experimental tests carried out for three different material densities. 2. The influence of densification on the fatigue behaviour of the densified material was determined by numerical modelling of the cyclic test. The commercial software package ABAQUS was used to perform the numerical simulations.