Joining of stainless steel (AISI 304L) to hot isostatically pressed alumina (HIP-Al₂O₃) using the braz-ing alloy 72Ag-28Cu was investigated. The microstructural characterization at various stages of joining, including metallization, annealing of overlaid Ni coating, and brazing, was comprehensively evaluated. The interface structure and the growth of phases were analyzed with optical microscope,scanning electron microscope, and electron probe microanalyzer (EPMA). Additionally, the leak tight-ness of these joints was assessed using a He-leak detector. Experimental results indicated the devel-opment of the manganese aluminate spinel (MnAl₂O₄) layer at the metallizing stage, which penetrated into HIP-Al₂O₃. The Ni overlaid coating further resulted in the formation of the Ni(Mo) solid solution layer followed by the Mo-rich phase. During the solid-state reaction and subsequent brazing cycle,the growth of the spinel layer close to HIP-Al₂O₃ was not adversely affected. The microstructure of the brazed joint was complex. It showed a eutectic structure within the brazed zone and a thin layer of Mo-rich, Ni-rich phases close to HIP-Al₂O₃. Increasing the brazing time resulted in the excessive growth of the thin layer that seriously affected the leak tightness of the joint.