The effects of alloying elements on microstructural features and mechanical properties in 0.55%C medium carbon steels were investigated. The samples were austenitized at 105$0^{circ}C$ for 30min. followed by quenching in a salt bath in the temperature range of 500 ~ $620^{circ}C$. The addition of Cr resulted in the decrease of the volume fraction of pro-eutectoid ferrite and interlamellar spacing in pearlite and the increase of strength. However, the addition of B caused the increase of the volume fraction of pro-eutectoid ferrite. Reduction of area and Charpy impact values were influenced by the combined effect of microstructural features, such as the volume fraction of pro-eutectoid ferrite, interlamellar spacing and the thickness of lamellar cementite in pearlite.