As a part of a research project that aims to develop a novel ironmaldng process using hydrogen flash reduction of iron ore concentrate, experimental determination of the phosphorus distribution ratio (L-p) between CaO-Mg-(saturated)-SiO2-Al2O3-FeO slag and molten iron was determined in the temperature range 1550-1650 degrees C. Oxygen partial pressure was controlled by H-2/H2O equilibrium in the range of 10(-10)-10(-8) Under these conditions applicable to the proposed process, L-p was 9-21. The proposed process is expected to produce iron with phosphorus content 7-14 times lower than in the iron produced by the blast furnace, considering the relative amounts of phosphorus inputs in the two processes and the low P content in the slag under the blast furnace conditions. This will decrease the need for dephosphorization in the steelmaking stage.