Introduction: Preeclampsia constitutes a significant complication during pregnancy, contributing notably to maternal and perinatal morbidity and mortality on a global scale. Calcium is vital for the functioning of vascular smooth muscle and the regulation of blood pressure. However, the association between maternal serum calcium levels and the severity of preeclampsia remains insufficiently elucidated, particularly within the context of Bangladesh. Objective: To evaluate the association between maternal serum calcium levels and the severity of preeclampsia among pregnant women at Dhaka Medical College Hospital. Methods: This cross-sectional observational study was conducted in the Department of Obstetrics and Gynecology, Dhaka Medical College Hospital, Bangladesh, from January to June 2026. A total of 120 pregnant women diagnosed with preeclampsia, categorized into non-severe (n=70) and severe (n=50) groups. Serum calcium levels were measured, and demographic, obstetric, and clinical characteristics were recorded. Data were analyzed using appropriate statistical tests, with p<0.05 considered significant. Results: Women with severe preeclampsia had significantly lower mean serum calcium levels compared to those with non-severe disease (7.82 ± 0.61 mg/dL vs. 8.64 ± 0.52 mg/dL; p<0.001). Serum calcium <8.5 mg/dL was strongly associated with severe preeclampsia (OR=4.5, 95% CI: 1.96–10.15, p<0.001), and this association persisted after multivariable adjustment (AOR=3.92, 95% CI: 1.64–9.37, p=0.002). Significant negative correlations were observed between serum calcium and both systolic (r=-0.49) and diastolic (r=-0.43) blood pressures. Conclusion: Low maternal serum calcium is linked to severe preeclampsia, suggesting it could help identify women at risk. However, causality can't be confirmed due to the study's cross-sectional nature. Longitudinal research with ionized calcium, vitamin D, and diet assessment is needed to clarify mechanisms before clinical use.