In this paper, we present the Compton profiles of Bi 2S 3 and Bi 2Se 3 using our 20 Ci 137Cs Compton spectrometer. To compare our experimental data, we have computed the Compton profiles, energy bands and density of states using linear combination of atomic orbitals with density functional theory (DFT) and Hartree-Fock (HF) scheme. It is seen that hybrid functional involving HF and DFT approximations gives a relatively better agreement with experimental momentum densities than other approximations of DFT. We have also reported the band structure, density of states, valence charge densities, dielectric functions and electron energy loss spectra using full potential linearized augmented plane wave scheme. On the basis of charge densities, Mulliken’s population data and equal-valence-electron-density profiles, Bi 2S 3 is found to be more ionic than Bi 2Se 3. The calculated dielectric functions for the parallel and perpendicular polarizations show a small anisotropic effect. The electron energy loss spectrum for Bi 2Se 3 is found to be in good agreement with the available experimental data.