Background: Extensive burn is characterized by high mortality.Many factors have been reported to affect the prognosis of major burn patients.Our aim was to identify the clinical features and analyze the mortality-related factors with extensive burn in a major fire in Kunshan, China on August 2, 2014.Methods: As an observational study, we studied a total of 167 burn patients were admitted to ICU of 18 tertiary hospitals in China.Epidemiologic and clinical characteristics, as well as therapeutic methods were recorded.The primary outcome was 90-dav mortality, with the secondary outcomes including 28-day mortality and 60-day mortality.The mortality-related factors were also analyzed.Results: Of the 167 patients, 62 (37.1%) patients died within 90 days.The median age was 38 years,the median burn size and full-thickness burn area were 95% and 82% total body surface area (TBSA) burns,respectively.71.3% patients with ≥ 90% TBSA burns, and 73.7% patients with full-thickness burns area over 50%.The survivors had lower APACHE Ⅱ, SOFA score, Baux index, earlier escharectomy and autologous skin graft, less c of them used of mechanical ventilation, CRRT and vasopressor.The 50% mortality rate (LA50) for TBSA and full-thickness burns area were 95.8% and 88.6%, respectively.The multivariate analysis showed that full-thickness burns area over 50% TBSA and residual burned surface area (RBSA)/total area-28d were strong predictors for mortality in burn patients (odds ratio, 2.55, 95% confidence interval [CI], 1.01 to 6.44, P =0.047;1.07, 95%CI, 1.04 to 1.09, P < 0.001, respectively).The ROC cutoff analysis for RBSA/total area-28d and RBSA/total area-60d to predict 90-day mortality were 62.5% and 24.0%, respectively.Conclusions: Burn size and full-thickness burns area were the main risk factors for poor outcome in massive young burns patients.Prompt surgical treatment combined with standardized and intensive life support in ICU may improve outcomes of extensive burns.