An austenitic heat resistant alloy, which comprises, by mass percent, C≦0.15%, Si≦2%, Mn≦3%, Ni: 40 to 80%, Cr: 15 to 40%, W and Mo: 1 to 15% in total content, Ti≦3%, Al≦3%, N≦0.03%, O≦0.03%, with the balance being Fe and impurities, and among the impurities P≦0.04%, S≦0.03%, Sn≦0.1%, As≦0.01%, Zn≦0.01%, Pb≦0.01% and Sb≦0.01%, and satisfies the conditions [P1=S+{(P+Sn)/2}+{(As+Zn+Pb+Sb)/5}≦0.050], [0.2≦P2=Ti+2Al≦7.5−10×P1], [P2≦9.0−100×O] and [N≦0.002×P2+0.019] can prevent both the liquation crack in the HAZ and the brittle crack in the HAZ and also can prevent defects due to welding fabricability, which occur during welding fabrication, and moreover has excellent creep strength at high temperatures. Therefore, the alloy can be used suitably as a material for constructing high temperature machines and equipment, such as power generating boilers, plants for the chemical industry and so on. The ally may contain a specific amount or amounts of one or more elements selected from Co, B, Ta, Hf, Nb, Zr, Ca, Mg, Y, La, Ce and Nd.