In this work the development of the technology and equipment for gas injection treatment of cast iron by inert gas (nitrogen) is presented. The equipment includes the plunging lance as a lined steel pipe with nozzles. The nozzles are thin channels, which are lined by ceramic tubes with small-diameter. The lance has a multiple use, as it has calibrated channel sizes, and provide the stability regime of gas injection treatment. The characteristic of the gas injection technology consists of blowing of melt by gas, which is injected into the liquid cast iron through thin jet with a speed near to the velocity of sound. In this case, the dispersion of gas jets in small-sized bubbles is reached, therefore the refining effectiveness increases. The gas injection treatment shows the promotion of casting properties, improvement of homogeneity and fineness of structure, stabilization or increasing of mechanical properties, decreasing of casting defectiveness. The positive effects of the gas injection treatment is the result of complex action of the injecting gas into the cast iron melt. Together with refining and homogenizing action at specified conditions, it offers the modifying and alloying effects also.