To investigate the degradation of mechanical properties induced mainly by neutron irradiation and operating temperatures, tensile tests were conducted from room temperature to 300°C using irradiated and unirradiated Zr-2.5Nb pressure tube materials. The irradiated longitudinal and transverse specimens collected from the coolant inlet, middle and outlet parts of the tube which had been operated in the CANDU reactor and showed different operating temperatures and irradiation fluence. The different tensile behavior was characterized by the tensile loading direction in the unirradiated tube. The transverse specimen showed higher strength and lower elongation than those of the longitudinal one. The increased strength hardening and the decreased elongation embrittlement of the irradiated material were compared to those of the unirradiated one. While the tensile strength of the inlet was higher than that of the outlet, the elongation of the inlet was lower than that of outlet. Considering the operation condition, it was proposed that the operating temperature could be a more effective parameter than the irradiation fluence for long-time life. Through TEM observation, it was also found that while the a-type dislocation density was increased, the c-type dislocation was not changed in the irradiated material. The fact that the higher dislocation density was sequentially distributed over the inlet to the outlet parts was consistent with the distribution of the tensile strength.