Obesity closely correlates with metaflammation and characterizes with systemic-chronic-low inflammation. This study aims to evaluate effects of C5a on the inflammatory response and insulin resistance in 3T3-L1 adipocytes. 3T3-L1 pre-adipocytes were induced to the mature 3T3-L1 adipocytes. Then, 3T3-L1 were intervened with anaphylatoxin C5a, lipopolysaccharide (LPS) and C5a+ LPS, respectively. Levels of Omentin, Chemerin, Vaspin and Apelin 12 in supernatants of medium were examined using ELISA. C5L2, C5a receptor (C5aR), I kappa B (IkB), IkB kinase (IKK), insulin receptor substrate 1 (IRS-1), IRS-2, PI3 K, p-PI3 K and beta-actin were examined using RT-PCR and western blot assay, respectively. C5L2-C5aR colocalization was identified using immunofluorescence double label. NF-kB expression or activity was evaluated using electrophoretic mobility shift assay (EMSA), dual luciferase assay and immunofluorescence assay, respectively. The glucose uptake and insulin sensitivity were also evaluated. Results showed that C5a intervention significantly enhanced inflammatory molecule levels in supernatants of 3T3-L1 adipocytes. IKK inflammatory signaling pathway participated in C5a induced inflammation of 3T3-L1 adipocytes. C5a triggered the colocalization of C5L2 and C5aR and activated the NF-kB inflammatory signaling pathway. C5a intervention in 3T3-L1 adipocytes decreased the glucose uptake and resulted in reduction of insulin sensitivity. Insulin signaling pathway participated in C5a caused insulin sensitivity reduction. C5a intervention triggered the phosphorylation of PI3 K. In conclusion anaphylatoxin C5a induced inflammatory response by activating TLR4/NF-kB signaling pathway and generating C5L2-C5aR dimer, and caused insulin sensitivity reduction by activating PI3 K signaling pathway.