Asthma is a common heterogeneous inflammatory chronic disorder of the airways. It is “defined by the history of respiratory symptoms such as wheeze, shortness of breath, chest tightness, and cough that vary over time and in intensity often with variable expiratory airflow limitation can be demonstrated”. According to the World Health Organization, asthma is the most common chronic respiratory disorder among children. Magnesium deficiency is associated with increased contractility of smooth muscle cells. Since contractility of bronchial smooth muscle is important in patients with asthma, magnesium deficiency could negatively influence the clinical condition. On the basis of the critical role of Mg in the regulation of bronchial smooth muscle, studies have shown that intravenous application or inhalation of Mg could alleviate symptoms in asthmatic patient. In the present study which was a case-control study plasma concentration of magnesium in 50 asthma patients (27 male, 23 female) in Gaza strip were measured and compare with 50 healthy non-asthmatic controls (37 male, 13 female). Questionnaire interview was applied. The concentrations of Mg were measured by using spectrophotometer. The mean±SD magnesium level in plasma was 1.52±0.4 mg/dl, 2.02±0.27 mg/dl in cases and control respectively, there was statically significant difference between cases and control (P=0.000). Thirty-nine (78%) of cases had Mg deficiency while seven (14%) of control had Mg deficiency. Seven (14%) of patient had sensitivity to dairy product (P=0.031). Forty-five (90%) of patient had health problems especially frequent inflammation of eyes, nose and throat (P=0.000). There were significant differences between cases and control in family history of disease (P=0.000). The finding of this study demonstrate that asthmatics patient had lower plasma magnesium level compared to healthy controls in Gaza strip.