A process for producing a high-alloy seamless tube, being characterized in that: a starting material to be extruded made of a high alloy comprising, in mass%, Cr: 20 to 30% and Ni: more than 22% and 60% or less is heated to a temperature predetermined according to the contents of Mo and W and subjected to a hot-extrusion process, the heating temperature satisfying a relationship of Formula,, or as below, which is expressed in terms of the average cross-sectional area of the starting material to be extruded, the extrusion ratio, and the extrusion speed: when 0 % ≤ Mo + 0.5 W < 4 %, T ≤ 1343 − 0.001322 × A − 1.059 × EL − 0.129 × V when 4 % ≤ Mo + 0.5 W < 7 %, T ≤ 1316 − 0.001322 × A − 1.059 × EL − 0.129 × V when 7 % ≤ Mo + 0.5 W, T ≤ 1289 − 0.001322 × A − 1.059 × EL − 0.129 × V where A and EL in Formulae to are determined by the following Formulae and: A = π × t 0 × d 0 − t 0 and EL = L 1 / L 0 given that each symbol in the above Formulae to means the following quantity: Mo: Mo content in the starting material to be extruded (mass%), W: W content in the starting material to be extruded (mass%), T: Heating temperature of the starting material to be extruded (°C), A: Average cross-sectional area of the starting material to be extruded (mm 2), EL: Extrusion ratio (-), V: Extrusion speed (mm/s), d 0: Average outside diameter of the starting material to be extruded (mm), to: Average wall thickness of the starting material to be extruded (mm), L 0: Length of the starting material to be extruded (mm), and L 1: Length of the extruded tube (mm). a starting material to be extruded made of a high alloy comprising, in mass%, Cr: 20 to 30% and Ni: more than 22% and 60% or less is heated to a temperature predetermined according to the contents of Mo and W and subjected to a hot-extrusion process, the heating temperature satisfying a relationship of Formula,, or as below, which is expressed in terms of the average cross-sectional area of the starting material to be extruded, the extrusion ratio, and the extrusion speed: when 0 % ≤ Mo + 0.5 W < 4 %, T ≤ 1343 − 0.001322 × A − 1.059 × EL − 0.129 × V when 4 % ≤ Mo + 0.5 W < 7 %, T ≤ 1316 − 0.001322 × A − 1.059 × EL − 0.129 × V when 7 % ≤ Mo + 0.5 W, T ≤ 1289 − 0.001322 × A − 1.059 × EL − 0.129 × V when 0 % ≤ Mo + 0.5 W < 4 %, T ≤ 1343 − 0.001322 × A − 1.059 × EL − 0.129 × V when 4 % ≤ Mo + 0.5 W < 7 %, T ≤ 1316 − 0.001322 × A − 1.059 × EL − 0.129 × V when 7 % ≤ Mo + 0.5 W, T ≤ 1289 − 0.001322 × A − 1.059 × EL − 0.129 × V where A and EL in Formulae to are determined by the following Formulae and: A = π × t 0 × d 0 − t 0 and EL = L 1 / L 0 given that each symbol in the above Formulae to means the following quantity: Mo: Mo content in the starting material to be extruded (mass%), W: W content in the starting material to be extruded (mass%), T: Heating temperature of the starting material to be extruded (°C), A: Average cross-sectional area of the starting material to be extruded (mm 2), EL: Extrusion ratio (-), V: Extrusion speed (mm/s), d 0: Average outside diameter of the starting material to be extruded (mm), to: Average wall thickness of the starting material to be extruded (mm), L 0: Length of the starting material to be extruded (mm), and L 1: Length of the extruded tube (mm).