The structural, electronic and dynamical properties of LaS compound in NaG (B1) and CsCl (B2) structures are studied by performing ab initio calculations within the generalized gradient approximation (GGA). The calculated lattice constants, static bulk modulus, first-order pressure derivative of the bulk modulus and band structures are reported in both NaCl and CsCl structures and compared with theoretical and available experimental results. The transition pressure for the B1 type to B2 type structure is calculated to be about 20.8 GPa. A linear-response approach to density functional theory is used to derive phonon dispersion curves and density of states. The calculated phonon spectra are in good agreement with available experimental results. A detailed discussion of atomic displacement pattern is also presented. (C) 2007 Elsevier B.V. All rights reserved.