A manufacturing method of power-module substrate (10), the power-module substrate (10) being obtained by joining a circuit layer (12) made of copper to one surface of a ceramic substrate (11) and joining a heat-radiation layer (13) made of aluminum to the other surface of the ceramic substrate (11), including: a circuit layer bonding step in which the circuit layer (12) is brazed on the ceramic substrate (11), a surface treatment step after the circuit layer bonding step in which a thickness of an oxide film on the other surface of the ceramic substrate (11) is made 3.2 nm or less at least at a peripheral part of an intended bonding area between the ceramic substrate (11) and the heat-radiation layer (13), and a heat-radiation layer bonding step in which the heat-radiation layer (13) is brazed on the other surface of the ceramic substrate (11) after the surface treatment step.