Background: Necromys lasiurus belongs to a group that includes New World rats and mice. The few studies concerning N. lasiurus consider this species to be a good experimental model because they adapt easily and because maintenance in captivity is low-cost. Moreover, Cricetidae are epidemiologically important as vectors of various diseases. The aim of the present study was to describe the macroscopic and microscopic features of embryonic and fetal development in this species. Methods: Totally, 8 embryos and 12 fetuses were used and allocated in 6 groups. Gestational age was determined by the crown-rump length (CR) and weight. After the gross descriptions, samples were processed for light microscopy. Results: The groups differed both macroscopically (due the characteristics related to the cervical curve, elongation of limbs and appearance of digits, closing of the auditory canal, blood vessels, elongation of the cranium, appearance of eyelids, skin thickness and coloration) and microscopically (the development of structures that constitute the facial region-mandibular, maxillary and nasal prominences). The structures preceding the appearance of the pituitary, lung, heart, brain cavity, fourth ventricle, liver development, the oral cavity, and layers that make up the cornea, retina, pigmented layer of the retina, and the lens were observed. Ossification of some regions was also observed. Conclusion: The results showed that embryonic stage is present until day 15 of gestation. After this, during the fetal life the individuals showed a quickly development and maturation of the internal organs. These morphological results in regard to the development of N. lasiurus, can be used as a standard for interpretation of experiments that use this species as a model in science, including too compared with pathological results in disturbed gestations that can affect the normal development.