The present work is dedicated to the description of the pseudo - binary Al 2 O 3 - Bi 2 O 3 and the isothermal section at 600°C of the system Al 2 O 3 - Bi 2 O 3 - PbO according to a Calphad approach. It takes part of the complete description of the complex system Pb - Bi - Fe - (Al,Cr) - O. Such study is of hig h interest for the nuclear community that aims to develop protective coatings for the MEGAPIE s pa l lation t arget to prevent the T91 steel from corrosion due to contact with lead - bismuth eutectic liquid.