The structural parameters, electronic, elastic, hardness and optical properties of oP(12)-type RuB2 (Space group Pnma, No: 62) are investigated by means of density functional theory method within local-density approximation as a function of pressure. It is shown that the results at 0 GPa pressure are in good agreement with related theoretical and experimental data. The pressure dependence of elastic constants, special bond lengths, Mulliken bond populations, hardness, energy band gaps, charge densities and optical properties such as dielectric function, absorption coefficient, reflectivity function, extinction coefficient, refractive index, energy loss spectrum of oP(12)-type RuB2 have been investigated. It is observed that the oP(12)-type RuB2 compound exhibits anisotropic compressibility under hydrostatic pressure: c-direction is more compressible than a- and b-directions, due to the different bond stiffness and bond angle changes. From calculated partial density of states, Mulliken populations and 2D/3D electron densities, the nature of chemical bonding for RuB2 can be recognized as a combination of partially covalent, ionic and metallic bonds. The calculated hardness value shows that oP(12)-type RuB2 is hard material.