Objective: To investigate the effect of lead exposure before pregnancy on bone lead mobilization and bone microstructure in pregnant rats, so as to provide the evidence for illustrating the potential mechanisms of bone lead mobilization during pregnancy. Methods: Twenty-six weaning female specific pathogen-free (SPF) rats of the Wistar strain were randomly divided into the exposure group and the control group. Rats in the exposure group were given 0.05% lead acetate solution for weeks, while animals in the control group were given 0.05% sodium acetate solution. Then, rats in both groups were given distilled water. Following removal of lead exposure for 4 weeks, female rats were co-caged with healthy males at the same age until pregnancy. The blood, femur and tibia specimens were collected from female rats on days 3 (GD3), 10 (GD10) and 17 (GD17) at pregnancy, and the blood and bone lead levels were measured using inductively coupled plasma mass spectrometry (ICP-MS). The unilateral rat femur was scanned using micro-computed tomography (micro CT), and the microstructure changes of cortical and trabecular bones were investigated. The structural and morphological changes of rat femur were observed using hematoxylin-eosin (HE) staining. Results: During the study period, satisfactory mental status and activity and good coat glossiness were observed in female rats in both groups, and there was no significant difference in the increase of rat body weight between groups. The blood lead level at GD17 and bone lead levels at GD3, GD10 and GD17 were significantly higher in rats in the exposure group than in the control group (P<0.05), and the trabecular bone lead level was significantly lower in rats in the exposure group at GD17 than at GD10 (P=0.015). The trabecular bone lead level correlated negatively with blood lead level (r=-0.578, P=0.049), and bone lead contributed 26.8% to blood lead. The bone mass, trabecular number, thickness and density of female rat trabecular bones all reduced in the exposure group at GD17, with an increase in trabecular space, and the proportion of trabecular areas reduced by 27.34% in the exposure group relative to the control group (t=2.851, P=0.046). Conclusions Lead exposure before pregnancy promotes the release of lead from trabecular bones into blood and affects bone microstructure in rats. There is bone lead mobilization during late pregnancy.