Liquid Metal Fast Breeder Reactor (LMFBR) fuel-sodium condensation aerosols which may be formed in a major reactor accident have been investigated. A pulsed beam from a high-powered C02 laser vaporized PuO2-UO2 from the surface of a rotating LMFBR fuel pellet. The PuO2-UO2 vapor rapidly condensed and coagulated into branched, chain-like aggregates. These aggregates were swept by argon into a sodium vapor atmosphere. The sodium condensed on the aggregates and the mixed aerosol was introduced into 50% relative humidity air. These aerosols have been characterized according to physical appearance, crystalline structure, and aerodynamic behavior. The mixed PuO2-UO2-Na aerosol appeared physically similar to sodium aerosol alone. X-ray and electron diffraction analyses indicated that no chemical interaction occurred between the PuO2-UO2 aggregates and sodium aerosol, or at least that the product of a reaction is amorphous, if they were kept in a fairly dry atmosphere; however, when exposed to water vapor, sodium uranyl tricarbonate was formed. The activity median aerodynamic diameter (AMAD) of the PuO2-UO2 aggregates was approximately 0.80 μm, depending somewhat on the energy input per laser pulse. The AMAD of the mixed PuO2-UO2-Na aerosol was higher than for the PuO2-UO2 aerosol alone, and increased as the sodium-to-mixed oxide ratio increased.