Purpose: Patients with chronic lung disease as asthma appear to be at increased risk for vitamin D deficiency for reasons that are not clear.  Methods: A cross sectional study including 75 asthmatic adults aged older than 18 years and 75 adults healthy control aged older than 18 years (35 males and 40 females for both groups) assessing the relationship between serum 25 hydroxy vitamin D levels and lung function.  Result: In our study only (12٫31%) of our asthmatic adults had sufficient vitamin D levels ( ≥ 30 ng/ml) , wherase (85%) of healthy control subjects expressed sufficient levels. Vitamin D deficiency (<20 ng/ml) was observed in 59 (78.66%) asthmatic patients (17.28 ±2.4 ng/ml). Deficiency was not observed in controls (33.67±6.3). In asthmatic patients Serum 25(OH) vitamin D was positively correlated with forced expiratory volume in 1 second %   (  FEV1 %) predicted &forced expiratory/forced vital capacity ratio ( FEV1//FVC)(P=<0.05 for all). There was no significant association between serum vitamin D level and eosinophil count. Conclusion: Reduced vitamin D levels are highly prevalent in adult asthmatic patients and are associated with impaired pulmonary functions