PURPOSE: To provide heat resistant steel for a high temp. gas furnace with enhanced corrosion resistance and high temp. strength in an inert gas, by a method wherein a specific amount of C, Si, Mu, Cu, Ni, Al, Mo are contained and Ti and Nb are further added to reduce the amount of Cr.

CONSTITUTION: This heat resistant steel for high temp. gas furnace consists of, on the wt. basis, 0.02W0.2% C, 0.05W2.0% Si, 0.05W2.0% Mn, 8W15% Cr, 8W 13.5% Ni, 0.3% or less Al, 3.5W8% Mo, 0.01W0.1 Ti and Nb respectively added alone or compositely and the remainder Fe and inevitable impurities. This constituent steel is one of which the amounts of Cr and Ni are reduced and a specific amount of Mo, Ti, Nb are added. By this composition, heat resistant steel for the high temp. gas furnace having excellent corrosion resistance and high temp. strength in an impure helium gas is inexpensively obtained.