Abstract: The influence of addition of high speed steel powder on the properties and microstructure of sintered steels has been studied. The aim of this research is to find out proper content of high speed steel powdes which will lead to an achievement of the optimum mechanical properties of the sintered samples. The results show that the optimum mechanical properties have been obtained with about 20% high speed steel powder addition. The addition of high speed steel powder will result in a decrease in both density and impact energy of the sintered steels. The hardness of the sintered steel increasses as content of high speed steel increases. The amount of retained austenit and the amount of martensite have a linear relationship with the content of high speed steel in the sintered steels. The martensite which is high in microhardness is mainly formed in the interconected areas between original high speed steel particles and original iron particles in the sintered steels.