Abstract: Objective To analyze the changes in serum procalcitonin (PCT) in patients with extremely severe burn and sepsis, and to evaluate its clinical significance in the prognosis of patients. Methods Thirteen patients with extremely severe burn and sepsis injured in the aluminum dust explosion accident, which occurred in Kunshan of Jiangsu province, were admitted to our unit on August 2nd, 2014. They were involved in this retrospective study and divided into death group (n=5) and survival group (n=8) according to the outcome. Acute Physiology and Chronic Health Evaluation (APACHE) Ⅱ score and Sequential Organ Failure Assessment (SOFA) score at post admission hour (PAH) 24 were compared among the patients between two groups. Serum level of PCT, serum level of C-reactive protein (CRP), white cell count, neutrophils, platelet count, level of aspartate transaminase (AST), level of prealbumin (PA), level of creatinine, level of urea nitrogen, and level of blood sodium were compared among the patients between two groups in post admission week (PAW) 1, 2, 3, and 4. Data were processed with Fisher's exact test, analysis of variance for repeated measurement, t test, and Mann-Whitney test. Receiver operating characteristic (ROC) curves of serum PCT values were plotted to evaluate the predictive value for death of 13 patients in PAW 3 and 4. Results The differences in APACHE Ⅱ score and SOFA score at PAH 24 and serum level of CRP, white cell count, level of AST, level of creatinine, level of urea nitrogen, and level of blood sodium from PAW 1 to 4 of the patients between two groups were not statistically significant (with t values from -1.164 to 0.587, Z values from -1.872 to -0.442, P values above 0.05). The serum levels of PCT in patients of death group in PAW 3 and 4 were respectively (15.8±14.9) and (13.6±5.6) ng/mL, which were significantly higher than those of survival group [(2.4±1.8) and (4.9±6.1) ng/mL, with Z values respectively -2.635 and -2.208, P<0.05 or P<0.01]. The serum levels of PCT of patients in death group and survival group in PAW 1 and 2 were close (with Z values respectively -0.732 and -1.025, P values above 0.05). Compared with those of survival group, neutrophils in PAW 4 was significantly increased (t=-3.690, P<0.01), the platelet count in PAW 4 was significantly decreased (t=4.858, P<0.01), and the level of PA in PAW 2 was significantly increased in patients of death group (t=-2.320, P<0.05). There were no statistically significant differences in neutrophils, platelet count, and the level of PA at the other time points of patients between death group and survival group (with t values from -1.562 to 1.904, P values above 0.05). The total areas under ROC curves of serum level of PCT for predicting death of 13 patients with extremely severe burn and sepsis in PAW 3 and 4 were respectively 0.938 and 0.906, and 7.45 ng/mL and 8.77 ng/mL were respectively chosen as the optimal threshold values, with sensitivity of 75.0% and 100.0% and specificity of 100.0% and 87.5%. Conclusions Serum level of PCT in PAW 3 and 4 can be used as the vital prognostic indicators for patients with extremely severe burn and sepsis, and it can be considered as a guide for rational treatment in clinic.