This paper investigates the effect of different carbon contents and cooling rates on gray iron tensile properties as well on the formation of different microstructure features. Four heats with increasing amount of carbon were cast. Every heat constituted of three cylinders, each of them surrounded by different materials which provided a wide range of solidification rates. The casting specimens were subjected to tensile test measurements and to microstructure examination. The results indicate a clear correlation between cooling rates, ultimate tensile strength (UTS), carbon content and eutectic cell size. Microscopic analysis shows also a relation between the primary phase’s fraction and the number of the eutectic cells.