Two types of ЭП741 pre-alloyed powder were prepared via vacuum induction melting gas atomization (VIGA) technique and plasma rotating electrode process (PREP) respectively. Then with the pre-alloyed powders, ЭП741 alloy was prepared via hot isostatic pressing (HIP) by 140 MPa at 1200 ^oC for 3 h. In the obtained ЭП741 pre-alloyed powders, there were defects such as inclusions and prior particle boundaries (PPBs) etc., as well as changes in the mechanical properties of the HIPed alloy caused by these defects. Hence, the above matters were systematically assessed by mean of scanning electron microscopy (SEM), while taking the deformed powder metallurgy alloy (PM billet + hot deformation) as a calibration. Results show that the PREP powder exhibited higher purity and fewer inclusions, and the mechanical properties of the HIPed alloy with PREP powder are better than those of the HIPed alloy with VIGA powder. It follows that the PPBs may primarily contribute to the differences in mechanical properties between the HIPed alloys and the deformed PM alloy. Furthermore, PPBs may deteriorate the mechanical properties of HIPed alloys both at room temperature and 650 ^oC, and the tensile properties of HIPed ЭП741 alloys are lower than those of deformed PM alloy. Notably, at cryogenic temperature (-196 ^oC), the PPBs can extend the crack propagation paths, and thus the effect of PPBs on mechanical properties is weakened. In summary, the average levels of tensile strength and elongation of the HIPed alloys are better than those of the deformed PM alloy.