Abstract	
	The most used models for assessment of activity of oxidic melts are regular, subregular and quasichemic. In the report was attested possibility of application of ionic melts statistic model on calculation of activity in system "FeO"-CaO-SiO2  by 1823 and 1873 K. Accounts of activities of FeO and CaO was achieved an satisfactory agreement of calculated and experimental statements. Calculated activities of SiO2 are below, probably in consequence of melt polymerisation and in consequence of difference of SiO2 in state of liquidus and solidus. Adjusted method is possible to use like first approximation for approaching method of chemical equilibrium calculation in system metal-matte-slag. For the wider application of this method is necessary its adapting for associated melts.