Background: Asthma is a heterogeneous disease, usually represented by chronic airway inflammation leading to variable respiratory symptoms and variable expiratory airflow limitation. Vitamin D has been shown to have several effects on the innate and adaptive immune systems that might modulate the severity of asthma exacerbations. Vitamin D deficiency and insufficiency is common in asthma patient, which causes frequent asthma attacks, respiratory tract infections, reduced lung function, poor asthma control, poor steroid responsiveness and severe asthma exacerbations. Objective: To determine serum vitamin D levels among asthmatic patients and to correlate them with the severity of bronchial asthma. Methods: A total of 50 patients with stable bronchial asthma between 18 to 60 years ages groups were included in the study. This Observational Study was conducted from April 2022 to December 2022 in Department of Respiratory medicine, Kamla Nehru Chest Hospital, Jodhpur. After taking proper clinical history and system examination, spirometry was done in each patient to obtain forced expiratory volume (FEV1), FVC and FEV1/FVC ratio for determination of the severity of asthma. Asthma control was assessed by using of asthma control questionnaire. Serum vitamin D level and absolute eosinophils count were measured in all participants. Results: In our study out of 50 cases, male patients (n=24) and female (n=26) which Association of Allergic history in Group with Severity of asthma was statistically significant (p=0.0240) and mean Vitamin-D Levels (ng/ml) was significantly higher in Mild [29.2182± 6.0880] compared to Moderate [23.3583± 5.2467] and Severe [14.9067± 5.1568] (p<0.0001). The mean Vitamin D Levels was significantly higher in “well controlled” [27.9071 ± 6.3191] compared to “partly controlled” [22.8706 ± 6.8941] and “uncontrolled” [17.2158 ± 7.0243] (p=0.0002). Conclusion: Vitamin D deficiency and insufficiency are highly prevalent in asthma patients in which prolonged duration of illness, frequently asthma exacerbation and poor asthma control. Hence, vitamin D is a useful for prevention and treatment of bronchial asthma