Defects in binary Fe3Al alloy and Fe3Al doped with Mo, Cr and Si were studied by positron lifetime and Doppler broadening with a coincidence technique. The additions of Mo and Cr to Fe3Al increase the defect concentration, while decrease the open volume of the defects, When Fe3Al is alloyed with Si, the defect concentration and the open volume of the defects increase simultaneously, The behaviours of Mo, Cr and Si in Fe3Al alloy have been discussed.