Abstract: Objective To investigate the association of serum complement C1QB with the severity of spinal cord injury(SCI) patients, in order to clarify the value of C1QB as a serum biomarker in predicting the severity of SCI.Methods Patients who were admitted to the Affiliated Hospital of Xuzhou Medical University due to simple spinal fracture(a control group, n=10) and spinal cord injury(a SCI group, n=46) from January 2022 to October 2022 were enrolled for a prospective and observational study. Their general clinical data and related hematological indexes were collected. Both groups were compared for the severity of SCI which was assessed by American Spinal Injuries Association(ASIA) injury scale. Furthermore, three patients were randomly selected from each group, and serum exosomes were extracted and verified. The profiles of serum exosome proteomic expression in the six patients were compared, and differential protein expression was determined by GO and KEGG enrichment analysis. The levels of differentially expressed protein were measured by ELISA, and the components involved were compared to select the target protein C1QB. The levels of serum C1QB in 56 patients were determined by ELISA. Moreover, Spearman correlation analysis and Kruskal Wallis test were performed to determine the relationship between serum C1QB level and ASIA score and grades.Results According to proteomics and bioinformatics analysis, there were 17 differential proteins in serum exosomes after SCI, and C1QB was the most significantly up-regulated differential protein. Compared with the control group, the levels of serum C1QB in SCI patients significantly increased(P＜0.001). C1QB level was independently correlated with ASIA score(r=-0.814, P＜0.001) and ASIA grade(r=-0.852, P＜0.001).Conclusions The expression of serum C1QB significantly increases after SCI, and serum C1QB levels are closely correlated with the severity of SCI patients. C1QB may be a serological marker to assess the severity of SCI patients.