Aim To investigate the mediating effect of sleep‐related problems on the relationship between depression and work–family conflicts (WFCs) among middle‐aged female workers. Design Secondary analysis of cross‐sectional study. Methods Overall, 15,718 female workers aged 40–65 years from the Sixth Korean Working Conditions Survey (KWCS) were included. Depression was assessed using the WHO‐5 wellbeing index; sleep‐related problems and WFCs were measured with five items on a Likert scale. The mediating effect of sleep‐related problems between depression and WFCs was analysed using model 4 of Hayes PROCESS macro for SPSS. Results There was a significant positive correlation between depression and both sleep‐related problems (r = 0.225, p < 0.001) and WFCs (r = 0.124, p < 0.001). Depression also had a significant effect on sleep‐related problems (β = 0.221, p < 0.001) and WFCs (β=0.061, p < 0.001). Sleep‐related problems had a significant effect on WFCs (β = 0.282, p < 0.001). The indirect effect of depression on WFCs by mediating sleep‐related problems was β = 0.062 (95% bootstrap confidence interval = 0.057–0.068). The study also confirmed the significance of the mediating effect of sleep‐related problems in the relationship between depression and WFCs.