The effect of chromium, aluminium and copper contents on the structures and mechanical properties of cast iron was investigated. 1) Mechanical properties were improved with the formation of ledeburite by chromium addition. The primary carbides dispersed in martensitic matrix contributed to high strength and wear resistance. 2) Small addition of aluminium decreased hardness of the cast iron. 3) The impact values were decreased by the formation of the double carbides but improved by the heat treatment. 4) Small addition of copper up to a certain level increased the hardness. Also impact values were considerably increased.