A YSZ/Al2O3 layered structure was successfully reactive air brazed using Ag-CuO fillers. The interaction mechanism between the filler and ceramics was systemically analyzed. The effects of filler composition on the interfacial microstructure and joint properties were investigated. Ag-CuO fillers possessed good wettability on the YSZ and Al2O3 ceramics. Ag had diffused into the ceramic substrates, but the width of the diffusion layer at the YSZ interface (similar to 10 nm) was narrower than that at the Al2O3 substrate (similar to 20 nm). Further HRTEM observations confirmed interatomic bonding between the CuO and the ceramics. The lattice mismatches at the Al2O3/CuO and YSZ/CuO interfaces were 0.98% and 2.97%, respectively. The filler alloy composition had a major influence on the microstructure and shear strength. The CuO phase preferentially precipitated at the Al2O3 interface. Consequently, the continuous CuO and CuAl2O4 layers gradually formed at the Al2O3 interface with increasing CuO content in the filler. The maximum shear strength (similar to 45 MPa) was obtained when the composition was Ag-8mol%CuO. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.