Objective:To investigate the complement C3a receptor 1 (C3AR1) expression in glioma and its mechanism in progressing malignancy.Methods:(1) The C3AR1 mRNA expression data and clinical information were obtained in 607 glioma patients from The Cancer Genome Atlas (TCGA) database and 656 glioma patients from Chinese Glioma Genome Atlas (CGGA) database; the differences in C3AR1 mRNA expression were analyzed among gliomas with different World Health Organization (WHO) grading. The overall survival and disease-free survival were compared between high and low C3AR1 mRNA expression patients obtained from TCGA database by Gene expression profiling interactive analysis (GEPIA). Gene body (GO) function analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of C3AR1 related differentially expressed genes were performed by DAVID database. Correlation of C3AR1 mRNA expression with immune cell infiltration was analyzed using TIMER online website. (2) The brain tissues from 3 non-tumor patients and 9 glioma patients surgically resected in Department of Neurosurgery, First Affiliated Hospital of Xinxiang Medical University from January 2019 to September 2021 were collected; the C3AR1 protein expression was detected by Western blotting. (3) The in vitro cultured U87 and U251 cells were divided into negative control group and C3AR1 knockdown group ( C3AR1 being knocked down by lentivirus transfection); and CCK-8 assay, plate cloning assay and Transwell assay were used to detect the proliferation rate, number of colony formation and number of membrane penetrating cells. Western blotting was used to detect the nuclear factor-κB (NF-κB) signaling pathway protein expressions. Results:(1) In TCGA database, the C3AR1 mRNA expression in gliomas of WHO grading II, grading III and grading IV increased sequentially, with significant differences ( P<0.05). In CGGA database, the C3AR1 mRNA expression in glioma of WHO grading IV was statistically higher than that in gliomas of WHO grading II and grading III ( P<0.05). GEPIA showed that the overall survival and disease-free survival in the low C3AR1 mRNA expression group were statistically higher than those in the high C3AR1 mRNA expression group ( P<0.05). GO function analysis and KEGG pathway enrichment analysis revealed that C3AR1 related differentially expressed genes were more enriched in such biological processes and signaling pathways as calcium homeostasis, membrane structural valves, proton transmembrane transporter protein activity, chemokine signaling pathway and NF-κB signaling pathway. TIMER showed that C3AR1 mRNA expression in glioblastoma and low-grade glioma was positively correlated with infiltration degrees of B cells, CD4 + T cells, neutrophils, macrophages and dendritic cells, and C3AR1 mRNA expression in glioblastoma was negatively correlated with infiltration degree of CD8 + T cells ( P<0.05). (2) C3AR1 protein expression in glioma tissues was significantly higher than that in non-tumor tissues. (3) Compared with the negative control group, the C3AR1 knockdown group group had significantly lower proliferation rate, smaller numbers of colony formation and membrane penetrating cells, and lower expressions of NF-κB, phosphorylated (p)-NF-κB, p-NF-κB inhibitory protein (IκB)α, p-I-κB kinase (IKK)α and N-cadherin, and significantly higher E-cadherin expression. Conclusion:C3AR1 is highly expressed in glioma and progresses malignancy through NF-κB signaling pathway.