The dispersibility of rare earth oxide particles, such as La2O3, Ce2O3 and Y2O3, in various solvents was evaluated. From the results, the relationship between the dispersibility and Hansen's solubility parameters (delta(d), delta(p) and delta(h)) of the solvents was investigated. To represent the dispersibility of particles in various solvents, the median diameters of the particles in the solvents were measured. The values of Hansen's solubility parameters of a hypothetical solvent producing optimal dispersion were estimated from the measured results. From the results, the dependence of estimated delta(p) values on dielectric constant of the particles and dependence of estimated delta(h) on isoelectric point of the particles were investigated. The dispersibility of rare earth oxide particles in various solvents can be evaluated by using the percentage contribution of Hansen's solubility parameters (f(d), f(p) and f(h)) in triangular charts. From the measured result, Hansen's solubility parameters of the hypothetical solvent producing the optimal dispersion of particles can be determined. These Hansen's solubility parameters of the hypothetical solvent differ according to the kind of particle. The deltap and delta(h) values of the hypothetical solvent producing the optimal dispersion of particles are reasonably correlated with the dielectric constant and isoelectric point of the particles, respectively.