{001} facet dominated BiOBr nanosheets are fabricated via a facile hydrothermal method in the presence of nitric acid without any organic additive and applied for CO₂ photoreduction. The concentration of nitric acid easily regulates the thickness of the obtained BiOBr nanosheets. When employing concentrations of 0, 0.1, 0.5, 1 and 4 M nitric acid, the corresponding surface area and percentage of exposed {001} facets of BiOBr-0, BiOBr-0.1, BiOBr-0.5, BiOBr-1 and BiOBr-4 nanosheets significantly increase in sequence. BiOBr-0 nanosheets are incapable of converting CO₂ into CO. However, BiOBr-0.1, BiOBr-0.5, BiOBr-1 and BiOBr-4 nanosheets show successively enhanced CO₂ photoreduction performance. Surprisingly, they exhibit high selectivity for converting CO₂ into CO with negligible generation of CH₄. In particular, BiOBr-4 shows the highest CO production rate of 4.45 μmol g⁻¹ h⁻¹ under simulated sunlight irradiation. The electronic structure analysis demonstrates that the conduction band minimum is significantly raised to endow BiOBr-4 with reduction power for CO₂/CO conversion, in comparison with the incapability of BiOBr-0. The breakthrough in CO₂ reduction of BiOBr-4 nanosheets is ascribed to the larger active surface area, higher electron transfer, more effective charge carrier separation and significantly raised reduction ability.