This study investigated the possible degeneration in cochlear morphology induced by preeclampsia (PE) and the therapeutic/preventive effect of vitamin D (Vit D) and magnesium sulfate (MgSO4) used separately and together on feto-maternal outcomes. We created PE in rats using a reduced uterine perfusion pressure (RUPP) animal model and recorded blood pressure (BP), embryonic survival (ES), and embryonic weight (EW) and evaluated cochlear morphology by electron microscopy. The PE group had elevated BP, a decreased number and weight of live pups, and significant degeneration in the cochlea compared to the sham group. In the PEV group, we observed significant beneficial effects of Vit D supplementation at 14.5 and 19.5 dpc in terms of BP (p < 0.05), EW (p < 0.001), and cochlear degeneration compared to the PE group. In the PEM group, BP (p < 0.05) and cochlear degeneration nearly reached the level found in the sham group. However, although the EW was statistically different in the PE group, it did not reach sham group levels. We also observed that BP returned to sham level (p < 0.01) and noticed significant increases in the EW (p < 0.0001) and ES (p = 0.017) in the PEMV group compared to the PE group. According to the scanning electron microscope results, combined administration of VitD and MgSO4 is more effective than separate administration in improving cochlear degeneration induced by PE. The administration of Vit D and MgSO4 during pregnancy has beneficial effects on PE pathology and may play a significant role in preventing PE-related complications, including cochlear degeneration.