Objective: To determine the association between body weight and COVID-19 outcomes.Methods: This is a retrospective cohort study of COVID-19 patients admitted in a dedicated COVID-19 hospital, a tertiary health care center, between May and June 2021. Demographic data and baseline variables, including age, sex, body mass index (BMI), and comorbidities were collected. Outcomes (death or mechanical ventilation) of the patients with different BMI, age, comorbidities, and qSOFA scores were compared. Besides, the risk factors for death or mechanical ventilation were determined. Results: The mean age of the subjects was (51.8±14.7) years old, and 233 (74.2％) were male. There were 103 (32.8％) patients with normal weight, 143 (45.5％) patients were overweight, and 68 (21.7％) patients were obese. In-hospital deaths and need of mechanical ventilations were significantly higher in the obese and the overweight group compared to the normal weight group, in age group ≥65 years compared to <65 years, in patients with ≥1 comorbidities compared to patients without comorbidities, in patients with qSOFA scores≥2 compared to patients with qSOFA scores<2. There was a significantly increased risk of death (RR: 4.1, 95％ CI 1.0-17.4, P=0.04) and significantly increased need of mechanical ventilation (RR: 5.2, 95％ CI 1.8-15.2, P=0.002) in the obese patients compared with those with normal weight after controlling other covariates. Conclusion: Obesity is one of the significant risk factors for adverse outcomes in COVID-19 patients and should be considered during management.