Knowledge of follicle development during pregnancy under experimental conditions could be a key factor to understanding maternal ovarian activity. Thus, this study evaluated the effects of maternal protein restriction before and during pregnancy on folliculogenesis. Swiss outbred female mice were allocated to either a control (CC; 20% protein) or treated (TT; 8% protein) group. Pregnant females were killed either on Gestational day (GD) 7.5 or GD17.5 and the ovaries were evaluated using histomorphometric and immunohistochemical methods. TT females showed higher feed and energy intakes, but lower bodyweight gain at GD17.5 (P <0.05). They also had lower number of secondary follicles at GD7.5 and a higher proportion of primordial follicles at GD17.5 (P <0.05). In addition, the areas of the secondary follicles and their granulosa layer were smaller in the TT group on GD7.5, whereas the areas of the oocyte and granulosa layer from atretic follicles were larger (P <0.05). Notwithstanding the slight increase in the insulin-like growth factor 1 (IGF1) receptor expression on GD7.5 in the TT group, there was a marked reduction in IGF1 expression detected in secondary follicles on GD17.5 (P <0.05). Collectively, these results demonstrate that protein restriction during pregnancy negatively affects follicle quality by reducing the size and activation capacity, which is more severe in late pregnancy.