The effects of extrusion temperature and pre-heat soak time for billets on the mechanical properties of Zr-2.5Nb pressure tubes for CANDU reactors have been examined. The β-quenched billets from a quadruple-melted ingot containing approximately 1200 ppm of oxygen were extruded at 780, 815, and 850°C with pre-heat soak times of 15 to 300 min. The extruded hollows were finished by cold drawing (with a 28% reduction in area) and then stress relieving at 400°C. The α-phase grain structure, tensile strength, and fracture toughness properties were found to vary with the pre-heat temperature and soak time. All the materials were tough because embrittling impurities were absent. The tubes with 780°C preheat had a very fine and uniform α-grain structure, giving high strength and toughness at all soak times. The opposite was true for the 850°C soaks; the grain structure was coarse and inhomogeneous and the materials tended to be less strong and less tough. The tubes with the 815°C soaks showed intermediate values of strength and toughness. These variations in mechanical properties are discussed in terms of α-grain refinement and oxygen enrichment.