As a new promising thermoelectrical material in the range of intermediate temperature, BiCuSeO attracts much attention due to the combination of low intrinsic thermal conductivity and relatively high Seebeck coefficient. In this study, the effects of substituting variable-valence rare-earth element Eu for Bi site on the microstructure and thermoelectric performance of BiCuSeO-based material were investigated. The results indicate that ions of two valence states, Eu²⁺ and Eu³⁺, coexist in the doped BiCuSeO samples. The doping of Eu not only improves the concentration of the carriers, but also modifies the band structure of BiCuSeO matrix, resulting in effective improvement of electrical transport properties. The electrical conductivity of Bi_0.85Eu_0.15CuSeO reaches 98 S·cm^-1 at 823 K, which is 6 times as high as that of the undoped sample. The power factor of 0.32 mW·m^-1·K^-2 and ZT of 0.49 can be achieved at 823 K for Bi_0.975Eu_0.025CuSeO sample. This study shows that the doping of variable-valence rare-earth elements can effectively improve the thermoelectric properties of BiCuSeO.