The present invention provides first resistant steel superior in fire resistance having less variation in material quality and exhibiting a yield strength of 2/3 or more of that at ordinary temperature even at 600°C and a method of production of the same, that is, fire resistant steel characterized by containing, by mass%, C: 0.01 to 0.03%, Mn: 0.2 to 1.7%, Si:0.5% or less, Cu: 0.7 to 2%, Mo: 0.8% or less, Nb: 0.01 to 0.3%, Ti: 0.005 to 0.03%, N: 0.006% or less, B: 0.0003 to 0.003%, V: 0.2% or less, Cr: 1% or less, Al: 0.1% or less, P: 0.03% or less, and S: 0.02% or less, containing Ni by mass ratio of Ni/Cu of 0.6 to 0.9, and comprising a balance of Fe and unavoidable impurities, and having a yield strength at 600°C of 60% of the yield strength at 21°C.