ATLAS is a general purpose experiment designed to exploit the full discovery potential of LHC. It consists of an inner detector immersed in a soleinodal magnetic field, hadronic and electromagnetic calorimeters and a muon spectrometer embedded in three air-core toroids. After a commissioning period with cosmic rays, ATLAS registered the first LHC proton-proton collisions at 900 GeV and 2.36 GeV center-of-mass energy in December 2009. Since 30 March 2010 the experiment is stably taking data at the energy of 7 TeV in the center of massd. The very good state of the ATLAS detector, performance study and first results with collision data are reported.