Treatment of mass production steels by cored calcium-containing wires is widely spread all over the world. Injection of several tens of gram of calcium per 1 t of the treated steel enables significantly improve its cast ability, increase the yield of CC billet, decrease rejection of rolled products by surface and internal defects, improve corrosion properties of steel and have similar effects. At the same time application of the technological method requires accurate forecasting of the purpose process conditions, strict following the technology parameters, application of quality injection equipment, as well as application of best calcium-containing cored wires. Taking into consideration, that the role of the filler in the cored wires is not discussed widely, the purpose of the work was summarizing of the experience of application of various calcium-containing materials. Mechanisms of calcium influence on steel quality considered. It was shown that it is possible to control not only chemical composition but also phase composition of nonmetallic inclusions by variation of calcium concentration in steel melt. Among others, liquid inclusions based on calcium aluminates which have high speed of surfacing, will be formed, thus ensuring deep steel refining for nonmetallic inclusions within a short time. Having high sulphur affinity, at the stage of continuous casting calcium forms sulfide and oxide-sulfide nonmetallic inclusions of micron and submicron size, uniformly distributed in the steel volume, which improves the structure of center zone of the continuously casted billet and that of the rolled product. It was shown that calcium-containing filler of a cored wire plays an important role in ensuring high and stable result. It was established based on the probes from tundish that the average recovery of fillers of electrolytic calcium is higher comparing with other fillers. Analysis of frequency distribution of the calcium recovery value showed that to ensure a guaranteed minimal content of calcium of 12 ppm at a CCM, it is required to inject aluminothermic calcium in the amount of 4.5 times bigger comparing with electrolytic calcium and ferrocalcium – 6 times bigger. Analysis of cast ability of steel treated by cored wires showed that to ensure a stable cast ability it is enough to add 55 grams of electrolytic calcium per 1 t of steel, at that addition of 83 grams of aluminothermic calcium does not ensure a stable casting from heat to heat. A dependence of rolled products rejection indices on calcium content in steel was noted, which indicated of a possibility of further increase of economic efficiency of technologies of steel mass production due to development of steel treatment by calcium.