An object of the present invention is to provide an Ni-based alloy pipe or tube for nuclear power with reduced rate of SCC crack propagation. The Ni-based alloy pipe or tube for nuclear power according to the present invention is an Ni-based alloy pipe or tube having a wall thickness of 15 to 55 mm, having a chemical composition of, in mass %: 0.010 to 0.025 % C; 0.10 to 0.50 % Si; 0.01 to 0.50 % Mn; up to 0.030 % P; up to 0.002 % S; 52.5 to 65.0 % Ni; 20.0 to 35.0 % Cr; 0.03 to 0.30 % Mo; up to 0.018 % Co; up to 0.015 % Sn; 0.005 to 0.050 % N; 0 to 0.300 % Ti; 0 to 0.200 % Nb; 0 to 0.300 % Ta; 0 % or more and less than 0.03 % Zr; and the balance being Fe and impurities, wherein the Ni-based alloy pipe or tube has a microstructure being an austenite single phase, and the chemical composition satisfies the following equation, Eq. (1): ˆ’ 0.0020 ‰¤ N / 14 ˆ’ Ti / 47.9 + Nb / 92.9 + Ta / 180.9 + Zr / 91.2 ‰¤ 0.0015 For the element symbols in Eq. (1), the contents of the corresponding elements in mass % are substituted.
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