Introducing the nanosecond phase into thermoelectric materials is an effective strategy to improve their thermoelectric properties. In this study, the influence of nano Y₂O₃ dispersion on the resistivity, Seebeck coefficient and thermal conductivity of Cu₂Se + x mol% Y₂O₃ (x = 0, 0.5, 1.0, 2.0, 3.0) was investigated. Their resistivity and Seebeck coefficient have no obvious change under the combined effects of the microstructure and the energy filtering. Especially, Y₂O₃ dispersion can inhibit the recrystallization of Cu₂Se and make the lamellar grains thinner, thus scattering phonon and reducing the thermal conductivity effectively. When x = 1.0, the thermal conductivity reaches a minimum of 0.65 W/K·m at 923 K. The dimensionless thermoelectric figure of merit (ZT) value of the Cu₂Se + 1.0 mol% Y₂O₃ sample reaches 1.81 at 923 K. The study indicates that nano rare earth oxides are relatively effective second-phase that can reduce thermal conductivity, which may be further promoted for other thermoelectric materials.