BiOBr nanosheets with dominant exposed (0 1 0) facets exhibit higher photocatalytic activity than those with highly exposed (0 01) facets under illumination of light with wavelengths (lambda) of similar to 365 and >= 420 nm, but lower photoactivity under light with lambda of 254nm. The lambda-dependent differences in photocatalytic activity result from different (0 0 1) facet exposure percentages (F(0 0 1)) and nanosheet thicknesses (H) between the two samples. Whether the difference in F(0 01) or that in H influences the photoactivity of the BiOBr nanosheets as a primary factor depends on incident light penetration depth which increases with the lambda. This study gives a better insight into the structure-performance relationship of two-dimensional (2D) photocatalysts and will supply important direction for photocatalytic studies of 2D semiconductors. (C 2016 Elsevier B.V. All rights reserved.