Major depressive disorder is a highly prevalent psychiatric condition often accompanied by disabling sleep disturbances, including insomnia and hypersomnia. Evidence suggests that magnesium, a vital trace element involved in neurotransmission, stress response, and circadian regulation, may play a crucial role in both mood and sleep. Low serum magnesium levels have been linked to increased depressive symptom severity and disturbed sleep quality. This study seeks to explore whether hypomagnesemia can serve as a biological contributor to sleep dysfunction in MDD. By employing the Beck Depression Inventory-II (BDI-II) and the Pittsburgh Sleep Quality Index (PSQI), as well as laboratory measurement of serum magnesium levels, the study aims to determine whether lower magnesium is significantly associated with greater depressive burden and poor sleep outcomes. The findings may help validate magnesium as a biomarker for early screening and risk stratification in psychiatric care.