The addition of a small amount of Sc to aluminum alloys improves their properties, such as strength, heat resistance, welding characteristics, decrease grain size. The beneficial role of Sc is attributed to a high density of coherent precipitates of the Al3Sc phase formed during decomposition of the solid solution at temperatures between 300 and 550°C. Alloying with Zr in addition to Sc improves both the grain-refining efficiency and thermal stability of the alloys. In the present work the phases and the sequences of their precipitation in Al-1%Mg-0.6%Si (in wt %) alloy with Sc and Zr additions has been studied. Two-step heat treatment was applied: the annealing in the temperature 350°C following by quenching from 540°C. Precipitation of the β′ (Mg2Si), cubic β (Mg2Si) and Al3(Sc,Zr) phases have been observed during the first step of annealing. Annealing at 540°C has led to dissolution of the Mg2Si precipitates and growing the particles of the Al3(Sc,Zr) phase. Analytical transmission electron microscopy and high resolution microscopy have been applied for the identification of phases, determination of particle sizes, their distribution and relationship between the phases.