Abstract Lα X-ray fluorescence (XRF) spectra emitted from some typical transition metals and their compounds showed different shapes characteristics of their chemical environments, which were Mn, MnO and MnO2, Fe, α-Fe2O3, Fe3O4 and FeSO4 and Cu, Cu2O, CuO and CuCl. Such change in spectral shapes was successfully explained, except for Cuo and CuCl, in view of the self-absorption scheme, where the DV-Xα molecular orvital calculation method was employed to estimate occupied and unoccupied density of states (DOS) responsible for X-ray emission and absorption. The Lα X-rays resulted from electron transition between an M 2p electron vacancy and occupied molecular orbitals including at least in part, M 3d orbitals of the atom of interest were theoretically explained to be absorbed by neighboring M atoms, where M means the same kind of transition elements, i.e. Mn, Fe and Cu. Here a part of the emitted Lα X-rays must be used to excite M 2p electrons to unoccupied molecular orbitals composed, at least in part, of M 3d.