In a method for desiliconizing pig iron prior to subsequent refining to steel molten steel slag after blast furnace tapping is charged onto the tapped pig iron bath, and optionally onto the blast furnace slag bath, in an amount corresponding to the Si content of the pig iron and the Fe and/or Cr oxide contents of the slag. The amount of steel slag is calculated such that the Si content of the pig iron is reduced to below 0.5% by weight at a simultaneous increase in the SiO.sub.2 content of the slag while reducing to liquid metals the Fe and/or Cr oxides of the slag. The slag-iron bath temperature is maintained at below 1500.degree. C.