First-principle calculations have been performed to investigate the structural and electronic properties of platinum group metal diborides in the stoichiometry XB 2 (X = Pt, Ir, Pd, Rh, Os). All investigated compounds have shown to belong to the orthorhombic Pmmn space group rather than the C2/m previously predicted in some of the compositions. Compressibility will reduce with boron addition in Pt, Pd and Rh, but will increase with boron addition into Ir and Os. The electronic density of states show that all the compounds are metals, with PtB 2 , PdB 2 and OsB 2 being potentially incompressible and superhard materials.