This work revealed that BiCuSeO oxyselenide is a potential oxide-based thermoelectric material, whose dimensionless figure of merit (ZT) reaches ∼0.70 at 773 K. High phase-purity BiCuSeO polycrystalline materials with fine grains were synthesized by a facile method combining a solid-state reaction and spark plasma sintering. Purifying the constitutive phase and reducing the grain sizes by introducing a high-energy ball milling process before spark plasma sintering were found to be effective in property enhancement. The resultant single-phased BiCuSeO sample derived from ball-milled powders shows good electrical conductivity above 4.0 × 103 S m-1 and a large Seebeck coefficient above 200 μV K-1. This compound has a low thermal conductivity (∼0.5 W m-1 K-1), which is associated with its low phonon transport speed and Young's modulus. Results indicated that BiCuSeO-based materials are promising for energy conversion applications in the moderate temperature range.