BiCuTeO is one of the potential thermoelectric materials owing to its low thermal conductivity and high carrier concentration. However, the thermoelectric performance of BiCuTeO is still below average and has a large room for improvement. In this study, we manipulated the nominal oxygen content in BiCuTeO and synthesized BiCuTeOx (x=0.94–1.06) bulks by a solid-state reaction and pelletized them by the cold-press method. The power factor was enhanced via the nominal oxygen deficiency due to the increased Seebeck coefficient. In addition, the thermal conductivity was reduced due to the decrease in lattice thermal conductivity owing to the small grain size that was generated by the deficiency in the nominal oxygen content. Consequently, the ZT value enhanced to around 11% at 523 K for the stoichiometric BiCuTeO0.94 compared to BiCuTeO. Thus, optimal manipulation of oxygen in BiCuTeO can enhance the thermoelectric performance. This study can be applied to developing the oxides with high thermoelectric performances.