In this study, magnetic arc oscillation (MAO) at three different frequencies (5 Hz, 10 Hz and 20 Hz) was applied during deposition of a Ni-base alloy, Hastelloy C276, by wire arc additive manufacturing (WAAM). The microstructure, surface finish and the mechanical properties of WAAM deposited Hastelloy C276 alloy samples with MAO were investigated and compared with the counterpart without the application of MAO. On-line monitoring of the arc movement and molten pool morphologies showed that the incorporation of MAO during WAAM may reduce the arc density during deposition, leading to a decrease in the solidification time. This, in turn, improved the surface accuracy of the as-built alloys. Furthermore, through the application of MAO, the dendrites exhibited a higher variety of growth orientations, and reduced dendrite arm spacings (DAS). The MAO at 5 Hz appeared to enhance the mechanical properties of the produced alloy, while the application at the higher frequencies of 10 Hz and 20 Hz led to less pronounced effects on the mechanical performance improvement. This study enhanced our understanding of the correlation of MAO processing-dendritic microstructure development-mechanical property for the Hastelloy C276 alloy prepared by WAAM, providing guidelines for the utilization of the MAO approach for tailoring the microstructure and the mechanical properties of WAAM produced alloys.