Although emerging data demonstrated mortality of young COVID-19 patients, no data have reported the risk factors of mortality for these young patients, and whether obesity is a risk for young COVID-19 patients remains unknown. We conducted a retrospective study including 13 young patients who died of COVID-19 and 40 matched survivors. Logistic regression was employed to characterize the risk factors of mortality in young obese COVID-19 patients. Most of the young deceased COVID-19 patients were mild cases at the time of admission, but the disease progressed rapidly featured by a higher severity of patchy shadows (100.00% vs 48.70%;P = .006), pleural thickening (61.50% vs 12.80%;P = .012), and mild pericardial effusion (76.90% vs 0.00%;P < .001). Most importantly, the deceased patients manifested higher body mass index (odds ratio [OR] = 1.354; 95% confidence interval [CI] = 1.075-1.704;P = .010), inflammation-related index C-reactive protein (OR = 1.014; 95% CI = 1.003-1.025;P = .014), cardiac injury biomarker hs-cTnI (OR = 1.420; 95% CI = 1.112-1.814;P = .005), and increased coagulation activity biomarker D-dimer (OR = 418.7;P = .047), as compared with that of survivors. Our data support that obesity could be a risk factor associated with high mortality in young COVID-19 patients, whereas aggravated inflammatory response, enhanced cardiac injury, and increased coagulation activity are likely to be the mechanisms contributing to the high mortality.