Boron (B) is usually used to produce p-type silicon to form the base layer in wafer-based silicon solar cells. The main objective of this work is to investigate the influence of B doping on the structural and mechanical properties of silicon. Using CASTEP program, which uses the density functional theory (DFT), with a plane wave basis, the structural, electronic, and mechanical properties of pure Si and the solid solution Si1-xBx (0.0001 <= x <= 0.05) were studied. The structure, density of states, band structure, and elastic properties were computed. It is found that as B concentration increases, the lattice constant increases, Bulk modulus (B), Shear modulus (G), and Young modulus (E) decreases. The ratio G/B decreases and Poisson's ratio (nu) increases. The decrease of G/B and increase of nu mean that brittleness of Si decreases by increasing B concentration.