This study presents an investigation of circadian lighting potential for a fibre optics daylighting system (FODS) in a single office in Beijing, China. Research methods included the monitoring of FODS daylighting performance during a 11-month period, the indoor lighting simulations at the horizontal workplane and vertical planes using a single office model, and thus the theoretical calculations of circadian stimulus brought by the FODS. Key findings are as follows: There is a high possibility that a proper level of circadian light at a windowless workspace could be achieved through applying the FODS in northern China. With this FODS, the non-visual effect of lighting (circadian system entrainment) can be attained when a standard lighting requirement was met at the horizontal workplane based on occupants' visual performance in this office. Compared with typical artificial lighting systems, the FODS can deliver circadian light in a more efficient way. In addition, it can be found that the application of FODS system would benefit office workers in terms of both visual and non-visual aspects. It is the first study to investigate the non-visual performance of a fibre optics daylighting system. •Investigation of Circadian Light potential of FODS in a single office in Beijing.•A 11-month monitoring of FODS in terms of daylighting performance in a lab.•Analysis of computational simulation and theoretical calculation for Circadian Stimulus.•Identification of a high potential of the FODS to achieve circadian entrainment.