The effects of adding Al, Y2O3 and the use of H2O as a PCA (process control agent), on the mechanical properties of mechanically alloyed Ni20Cr20Fe5Nb alloy were studied. The addition of Y2O3 and Al caused an increase in the tensile strength at room temperature, 400°C and 600°C. However, it was confirmed that the increase of tensile strength at room temperature and 400°C was predominantly caused by addition of Y2O3, while that at 600°C was mainly due to addition of Al. These results can be attributed to the dispersion strengthening of Y2O3, preventing the formation of Cr2O3 and the change of fracture mode at 600°C by the addition of Al. Therefore, the Ni20Cr20Fe5Nb2Al alloy using H2O as a PCA showed superior tensile strength at room temperature, 400°C and 600°C. The increase in the tensile strength at room temperature and 400°C can be attributed to the strengthening of the solid solution induced by the increase in the amount of Nb solid solution, resulting from the prevention of NbC formation, while the increase in the tensile strength at 600°C can be attributed to the strengthening of the grain boundary afforded by the presence of Al1.54Cr0.46O3 formed by the addition of Al. After aging treatment for 10 hours at 600°C, g²(Ni3Nb) precipitates were formed in the Ni20Cr20Fe5Nb2Al alloy in which H2O used as the PCA, and the formation of these precipitates caused an increase in hardness.