The Japanese traditional steel making method which manufactures steel "Kera" or pig iron "Zuku" from iron sand and charcoal is so called "Tatara" steel making process. The influence of the loading ratio of iron sand to charcoal on the "Tatara" steel making was investigated. In the case of the loading ratio is equal to 1, high carbon steel "Kera" was produced at the high yield accompanied with viscous slag "Noro". In the meantime, in the case of the loading ratio is equal to 1.5, the carbon content of the produced steel "Kera" was low at the low yield accompanied with a lot of low viscous slag "Noro". In the case of low loading ratio, so called "light charge", iron sand was well deoxidized and carbonized in the furnace and became to high carbon steel "Kera" at the high efficiently. In that case, the slag "Noro" became to viscous one because of the reduction of FeO content.
On the contrary, in the case of high loading ratio, so called "heavy charge", the deoxidization of iron sand was insufficient and most of iron sand was discharged as a slag "Noro" to the outside of the furnace. As the result, produced steel "Kera" yield lowered. During the "heavy charge" operation, the composition of the slag "Noro" became FeO-rich, and then the fluidity of the slag "Noro" increased. It was clarified that the controlling of the loading ratio was an important factor which affected both to the quality and productivity of steel "Kera" and the fluidity of slag "Noro" on "Tatara" steel making process.