Method and top blowing lance for decarburization refining chromium molten ferrous metal in which dust formation and chromium loss due to oxidation are suppressed and high productivity is achieved. Decarburization of molten ferrous metal is achieved by blowing gaseous oxygen into the molten metal in a refining furnace provided with a top blowing lance having a plurality of gas blowing nozzles at the tip of the lance. The gas blowing nozzles include at least one sub-nozzle provided at or near the lance axis and a plurality of main nozzles at an outer section of the lance. Blowing refining is carried out with oxygen flow from a plurality of the main nozzles at a flow rate higher than that from the sub-nozzle(s), when the carbon content in the molten metal is about 1 wt % or more.