Abstract : The NEMO-3 experiment searches for a neutrinoless double beta decay signal (beta beta 0 nu) with an expected sensitivity in terms of the half-life limit of the order of 1024 years. The discovery of this signal, forbidden in the Standard Model, would imply the violation of leptonic number conservation and would allow to determine the nature of this particule (Dirac or Majorana) and measure the neutrino mass scale. The goal of this work is to study high energy events from 82Se and 150Nd beta beta decay used in NEMO-3 detector. The first part of this work consists in the elaboration of a background model using NEMO-3 data. In the second part, the beta beta 2 nu half-life and a lower limit of the beta beta 0 nu half-life are computed using massive Majorana neutrino exchange hypothesis. In the last part, the measurement of some specific thallium contamination is performed thanks to the NEMO-3 capability to detect the 212Bi-Po decay.