Provided is an austenitic heat resistant alloy capable of exhibiting sufficient molten-salt corrosion resistance even when exposed to a molten salt of 600° C., and a production method thereof. The austenitic heat resistant alloy includes a base metal and a Fe—Cr—Ni—W film on the surface of the base metal. The base metal has a chemical composition consisting of: C: 0.030 to 0.120%, Si: 0.02 to 1.00%, Mn: 0.10 to 2.00%, Cr: 20.0% or more to less than 28.0%, Ni: more than 35.0% to 50.0% or less, W: 4.0 to 10.0%, Ti: 0.01 to 0.30%, Nb: 0.01 to 1.00%, sol. Al: 0.0005 to 0.0400%, and B: 0.0005 to 0.0100%, with the balance being Fe and impurities. The Fe—Cr—Ni—W film contains, as oxides, Fe: 15.0 to 35.0 at %, Cr: 15.0 to 35.0 at %, Ni: 10.0 to 45.0 at %, and W: 0.5 to 16.5 at %.