The behaviour of alloyed and unalloyed sintered steels in static and dynamic loading is influenced by their macro and microstructure. The characteristics of the used powder, their chemical composition, the conditions of shaping by pressing, and the parameters of the sintering process are some factors determining the structure of the steels [1, 2]. Under the same technological conditions, sintered materials were produced using iron powder of different particle size or in different powder mixtures for establishing the structure influence on some mechanical properties, The results obtained shows that the sintered materials present a higher sensitivity towards the dynamic and variable loads . In the same time, it was shown that a material made from a fine powder fraction behaves, at mechanical loads, almost in the same way as an elaborated material from the same powder but with a wider particle size distribution or particles size. Using of the different powder mixtures lead to some microstructures with better mechanical properties at the intergranulars necks. Using the copper powder or the low or high alloyed iron powder in a mixture with the basic iron powder determines an improvement of the mechanical properties by changing the materials microstructure. It was found that the addition of high alloyed steel powder has the strongest effect on the fatigue resistance.