A hearth structure of an oxygen-bottom-blowing converter comprises hearth bricks including a number of brick row units, each of which is provided with or without one tuyere therein to eliminate thermal stresses otherwise be caused by two tuyeres included in one brick row unit. The hearth bricks preferably include at least one row of bricks not including a tuyere arranged between the brick row units. Bricks around tuyeres are unburned magnesia-carbon or magnesia-dolomite-carbon bricks including an amount of carbon 7-35%, preferably 10-30% or the most preferably 20% by weight and including magnesia or magnesia-dolomite as grains and thicknesses of refractory mortar as joints between the bricks corresponding to 0.5-2.5% of the maximum width of the bricks, thereby improving the durability of the hearth structure and hence the converter.