The reaction between BaO (barium oxide) and Al2O3 (aluminum oxide) will result in the formation of BaAl2O4 (barium aluminate) according to the following equation:

3BaO + Al2O3 → BaAl2O4

This is a double displacement reaction where the barium cations in BaO switch places with the aluminum cations in Al2O3 to form the product BaAl2O4.