The physical and nuclear properties of EU2O3 were reviewed, evaluated, and compared with those of the other potential control materials for breeder reactors. Europia with a 90% theoretical density has approximately the same amount of europium atoms per unit volume as the pure metal. Consequently, the reactivity worth per unit volume of Eu2O3 is similar to that of pure metal. In addition, the reactivity of EU2O3 is superior to tantalum and is comparable to natural B4C. The decay heat of Eu2O3 is much lower than that of tantalum over the range of decay times that is of interest with respect to handling. Irradiation-induced swelling of EU2O3 is lower than that of B4C, and postirradiation examination revealed only ∼1% dimensional changes in the thermal- and/or fast-neutron spectrum (8 × 1025 n/m2). Although surface reaction between EU2O3 and the fast test reactor reference cladding Type 316 stainless steel leads to the formation of a europium silicate, it is expected that Eu2O3 would be compatible with low-silicon Type 316 stainless steel. In addition, the Eu2O3-sodium system was also shown to be compatible under simulated liquid-metal fast breeder reactor conditions without significant change. Consequently, Eu2O3 is an excellent alternate candidate compared to B4C as the neutron absorber for fast breeder reactors.