Background: Gestational diabetes mellitus (GDM) is one of the most common pregnancy complications that can affect the organ systems of the body in both the mother and fetus. This study aimed to determine the impact of mild GDM on maternal and fetal liver histopathological alterations. Materials and Methods: In this experimental study, 20 pregnant Wistar rats were randomly allocated in control and diabetic groups. Mild hyperglycemia was induced by intraperitoneal injection of streptozotocin (40 mg/kg body weight) on the 5th day of gestation. The control group received an equal volume of citrate buffer. The diabetic state was confirmed by a blood glucose level of 120–300 mg/dL. Maternal and fetal liver samples were obtained on day 19 of gestation and stained with hematoxylin and eosin for histopathological investigation. Results: Liver sections of diabetic dams exhibited edematous hepatocytes and scattered pyknotic and necrotic cells with dilated sinusoids and congested central veins. The portal tracts showed the proliferation of bile ducts with mild chronic inflammatory cells infiltrating together with fibrosis beyond the limited plate which extends to the central vein (porto-central fibrosis). Liver sections of their fetuses revealed edematous hepatocytes with increased necrotic cells, with pyknotic nuclei, dilatation of the hepatic sinusoids, and their central veins. There was also a relative increase in megakaryocytes, which promoted fibrosis and distorted vascular beds of the hepatic tissue. The portal tracts also showed bile duct proliferation. Conclusion: This study highlighted the adverse effects of uncontrolled mild GDM on liver structure in rat dams and their fetuses.