Abstract : In this thesis, I present my work in the CMS experiment on a search for the standard model Higgs boson decaying into a pair of tau leptons. The original goal and the final aim of this research is a contribution to the discovery of the Higgs boson at the LHC. After a summary of the theoretical framework and of the experimental apparatus, I will describe the particle-flow technique developed for the offline CMS event reconstruction. Tau reconstruction and identification in CMS are described. Particular emphasis is devoted to the discrimination between the electrons and tau leptons decaying semi-leptonically (giving hadrons and neutrinos). A crucial and challenging aspect in the search for the Higgs boson decaying into tau leptons is the reconstruction of the di-tau mass. On this subject, I have provided original contributions in the development of a new likelihood-based technique, called SVfit, which is then used for the analysis. Finally, a search for the Standard Model Higgs boson in the di-tau channel, based on 4.9 1/fb of pp collisions at sqrt(s) = 7 TeV, is presented. Events are selected where one tau decays semi-leptonically and the other decays fully- leptonically into neutrinos and lighter charged leptons (electrons or muons). No significant excess over the Standard Model backgrounds is observed. The statistical interpretation of the results is then translated into 95% CL upper limits on the signal cross-section.