Humans are exposed to numerous endocrine disrupting chemicals, including di(2-ethylhexyl) phthalate (DEHP). DEHP is regularly found in household items and consumer products. Unfortunately, DEHP is a reproductive toxicant, but few studies examine the direct impact of DEHP exposure on ovarian function during pregnancy. High fat diets are extremely prevalent amongst western cultures and they can also contribute to toxicity and endocrine disruption in the body. Therefore, this study focuses on the effect of both DEHP exposure and a high fat diet on ovarian steroidogenesis in pregnant mice. CD-1 female mice were split into four different groups: group one was given control diet and vehicle, group two was allotted DEHP (20 µg/kg/day) and control diet, group three was allotted the vehicle and a high-fat diet, and group four was allotted DEHP and a high-fat diet. CD-1 female mice were fed according to their group and mated with CD-1 male mice. After mating, the mice were then dosed with 20 µg/kg/day of DEHP or vehicle control (corn oil). Pregnant dams were euthanized at gestation day 13 or 16 and whole ovaries and sera were collected. From frozen ovaries, the steroidogenic enzymes were quantified by qPCR and sex steroid hormone levels were measured using an enzyme linked immunosorbent assay (ELISA) from the sera. Analysis from qPCR showed that DEHP and a high-fat diet exposure alter gene expression of steroidogenic regulators, specifically Cyp11a1, Cyp17a1, and Star at GD 13 and 16. ELISA analysis resulted in a significant change in testosterone in the high-fat only group. Overall, the results show that DEHP and a high-fat diet alter ovarian steroidogenesis in pregnant mice.