Background: Severe acute respiratory syndrome corona virus 2 (SARS-CoV-2), causing COVID-19, manifests with outcomes ranging from mild to severe, even fatal. The reason for severe symptoms remains unclear. Vitamin D is implicated in the pathogenesis of severe COVID-19, including ARDS, cytokine storms, and thrombotic complications. The aim of this study was evaluation of vitamin D status and its association with the severity of COVID-19 patients attending Bangabandhu Sheikh Mujib medical University (BSMMU). Methods: This cross-sectional study, conducted at BSMMU, Dhaka from January to December 2021, included 103 adult COVID-19-positive patients from both genders. Disease severity was assessed using WHO guidelines, and vitamin D levels recorded. Data were collected using a pre-designed datasheet after obtaining written informed consent. Results: Among 103 COVID-19 patients, 55.3% were vitamin D deficient, 26.2% insufficient, and 18.4% sufficient. Most were male (65%) in their sixth and seventh decades. The mean vitamin D level was 20.97±10.96 ng/ml with a median of 18.10 ng/ml. Vitamin D deficiency was highest among critical patients (84.6%), followed by severe (71.1%), moderate (41.9%), and mild (28.6%) cases (p<0.001). Severe patients had a significantly higher deficiency rate (74.5%) compared to non-severe (36.5%) cases (p<0.001). Symptoms such as cough (96.5%), fever (89.5%), and shortness of breath (78.9%) were prevalent in the vitamin D deficiency group. Conclusions: This study reveals a 55% prevalence of vitamin D deficiency in COVID-19 patients, correlating independently with disease severity. Hypertension and diabetes are notable comorbidities. It underscores the importance of assessing vitamin D levels in clinical practice.