We analysed Al-Li based alloys by means of atom-probe. The influence of parameters such as the tip temperature and the pulse fraction on the apparent composition were investigated for an Al-2.7at%Li alloy and for an Al-7.5at%Li-1.2at%Cu alloy. A ternary Al-3.5wt%Li-3.6wt%Mg alloy aged 24h at 190° C was studied. Atom-probe results point out the presence of Mg in the δ' phase