The developing uterus is highly sensitive to a brief exposure to different substances, in particular those with endocrine-disrupting activity. Thus, exposure to environmental, nutritional, chemical, and other xenobiotic factors affecting signaling events during critical organizational periods can alter the normal course of uterine development with lasting consequences. In this chapter, we provide an experimental protocol to evaluate the development of the rat uterus as a toxicity biomarker at two different developmental time points: (1) the neonatal period, on postnatal day (PND) 8, and (2) the prepubertal period, on PND21. In this experimental approach, we propose to assess: (1) uterine morphology and cytodifferentiation, (2) uterine cell proliferation, and (3) the expression of proteins involved in uterine organogenetic differentiation. All these morphological and molecular markers are useful tools to determine the consequences of exposure to toxicants with the potential to disrupt the uterine development.