Uranium oxide aerosols generated by resistance heating of UO2 pellets were characterized. The aerosols followed a bimodal size distribution, yielding 15–36% particles in a larger size range (2.1–11 μm) with a mass median aerodynamic diameter (MMAD) of 4.8 μm (σg = 2.3) and 64–85% particles in the smaller size range (0.43–2.1 μm) with an MMAD of 0.78 μm (σg = 1.8). The SEM photographs of the aerosols collected on various stages of an Andersen sampler revealed the presence of two types of particles, viz. individual spherical particles in the larger size range and cluster aggregates of very small primary particles in the smaller size range. The X-ray diffraction studies showed that the composition of the aerosols corresponds to U3O8 with small amounts of UO2 present in it. The relative concentrations of U3O8 and UO2, estimated from chemical analysis, were found to be 92.8 and 7.2%, respectively. In vitro solubility studies in a lung serum simulant showed that nearly 78% of the aerosols were dissolved within 75 days. The X-ray diffraction pattern of the collected particles remaining after 75 days dissolution showed that the relative concentration of UO2 was increased to nearly 29% from its initial value of 7.22%. Using these data, the dissolution halftimes of U3O8 and UO2 have been calculated and were found to be 29.8 and 606.5 days, respectively.