Highly porous ceramics are critical components of Solid Oxide Fuel Cells. Nevertheless, their mechanical properties are poor and not fully understood. Herein, Discrete Element simulations are used to quantitatively assess the relation between the particulate microstructure of highly porous ceramics and their mechanical properties. Partially sintered ceramics are numerically generated with complex microstructures including pore formers and bilayers. These microstructures are then tested in tension and compression to obtain their elastic and fracture behavior. Compiling experimental data from the literature and simulations results, an Orowan-Petch type relation between strength and particle size is proposed for highly porous ceramics. It is based on the local fracture model at the length scale of solid bonds between sintered particles.