Einsteinium(III) oxide is an oxide of the synthetic actinide einsteinium which has the molecular formula Es<sub>2</sub>O<sub>3</sub>. It is a colourless solid.
Three modifications are known. The body-centered cubic form has lattice parameter a = 1076.6 ñ 0.6 pm; this allows the ionic radius of the Es<sup>3+</sup> ion to be calculated as 92.8 pm. The other two forms are monoclinic and hexagonal: the hexagonal form has the lanthanum(III) oxide structure.
Einsteinium(III) oxide can be obtained by annealing einsteinium(III) nitrate in sub-microgram quantities.