Sunset Yellow (SY), a synthetic food dye, is widely used in the food industry worldwide. The acceptable daily dosage for SY is 2.5 mg/kg/bw in humans. If SY is consumed in overdosage, it may cause histopathological effects in several organs. Studies in the literature about the effects of SY on growth and development in mammals are contradictory, and there are not enough of them. The investigation aims to determine SY's effects on the stomach and small intestine in different age groups of mice using histological methods. Control and treatment groups were created via mice aged 4, 8, and 10 weeks (n = 6). SY was administered by gavage at a level of 30 mg/kg/bw for 28 days to treatment groups. On the last day of the study, the mice were weighed and sacrificed by cervical dislocation. Stomach and small intestine tissues were removed from mice and transferred to 10 % formaldehyde. After passing through alcohol and xylene series and staining with Hematoxylin-Eosin, the tissues were evaluated under light and electron microscopy. The mean body weight (p = 0.01), mean stomach weight (p = 0.03), and mean small intestine weight were increased (p = 0.02) in treatment groups. In these groups, ruptures, fractures, and hemorrhage were detected in the small intestine tissue. In the stomach tissue, necrotic areas and hemorrhage were detected among the epithelial cells. The degenerations were more advanced in the weaning group. SY may be more harmful during weaning and puberty, but additional long-term studies are needed on the subject.