Objectives: It is well-known that the complement system plays an essential role in host immunity. Observational studies have indicated that complement system-related molecules such as complement factor B (CfB) and other components are correlated with obesity and/or insulin resistance parameters. In this study, we investigated the role of adipocyte-derived CfB in adipose tissue metabolism. Methods: We investigated the expression level of complement system-related genes in adipocytes. To understand the role of CfB in adipocyte, we performed Cfb overexpression in 3T3-L1 preadipocytes and generated adipocyte-specific Cfb transgenic mice. Results: Cfb expression was markedly enhanced in 3T3-L1 adipocytes co-cultured with macrophages following endotoxin stimulation. In Cfb-overexpressing cells, the expression of adipocyte differentiation/maturation-related genes encoding peroxisome proliferator-activated receptor gamma (Ppar gamma), adipocyte Protein 2 and perilipin was significantly enhanced. Cfb transgenic mice showed a marked increase in the expression of genes encoding Ppar gamma, perilipin, sterol regulatory element-binding protein 1 c, and Cd36 in the subcutaneous adipose tissue. Conclusions: CfB plays a crucial role in late-phase of adipocyte differentiation and subsequent lipid droplet formation. (C) 2017 Elsevier Inc. All rights reserved.