Here, we introduce Ag substituted octacalcium phosphate (OCP-Ag) blocks with interconnected porous structure and sufficient mechanical strength as bone substitute (i.e., foam). We employed a two-step process for fabrication, which includes a setting reaction for acidic calcium phosphate granules using an acidic phosphate solution and a phase conversion process via dissolution-precipitation method in cocktail ((NH 4 ) 2 HPO 4 -NH 4 NO 3 -NaNO 3 -AgNO 3 ) solutions. The Ag contents in the fabricated OCP-Ag foams were 0.08–0.15 at%, which were sufficient in exhibiting contact antibacterial ability. The mechanical strength and porosity of the OCP-Ag foams were about 0.5 MPa and 70%, respectively. These values were sufficient for the application of the OCP-Ag foams as bone substitute. Graphical abstract