The Standard Model process of ttbar production is one of the most important backgrounds to searches for Supersymmetry (SUSY) at the Large Hadron Collider (LHC) at CERN. We describe the methods to estimate the contributions of ttbar decay with one and two leptons in SUSY searches with zero, one or two isolated leptons, multi-jets and large missing transverse energy with the first data of the ATLAS experiment. The performance has been evaluated with simulated data
