Abstract
In the current cosmological model, the Universe is predominantly composed of dark matter, the nature of which remains unexplained by the Standard Model of particle physic. Annihilation of particles of within new theoretical frameworks might induce a very high energy gamma-ray signal, observable by gamma-ray astronomy experiments. Largely dark matter dominated, dwarf spheroidal galaxies are privileged targets for such indirect search. The H.E.S.S. telescopes network discussed in the rst part of this work is a perfect example of atmospheric stereoscopic imaging experiment allowing to search for dark matter. A new discrimination method between electromagnetic and hadronic showers enhancing searches of weak sources is presented. It is applied to the Sagittarius dwarf galaxy observation data and the upper limit on the incoming gamma-ray ux is calculated. In orbit aboard Fermi's satellite since June 2008, the LAT conversion pair telecope enable dark matter search on the whole sky. Theoretical sensitivity to detect a dark matter signal is determined for two specic galaxies. At the end of the rst year of observations, upper limits on gamma-ray fluxes are derived for a catalog of dwarf spheroidal galaxies. Models of physic beyond the Standard Model are compared with calculated constraints on annihilation cross sections function of the mass paricles obtained from observations made with both experiments.