Free fatty acids (FFAs) are not only essential nutrient components, but they also function as signaling molecules in various physiological processes. In the progression of genomic analysis, many orphan G-protein coupled receptors (GPCRs) are found. Recently, GPCRs deorphanizing strategy successfully identified multiple receptors for FFAs. In these FFA receptors (FFARs), GPR40 (FFAR1) and GPR120 are activated by medium- to long- chain FFAs. GPR40 is expressed mainly in pancreatic β-cell and mediates insulin secretion, whereas GPR120 is expressed abundantly in the intestine and regulates the secretion of cholecystokinin (CCK) and glucagons-like peptide-1 (GLP-1), it promotes insulin secretion. Due to these biological activity, GPR40 and GPR120 are potential drug target for type 2 diabetes and selective ligands have been developed. In this review, we provide recent development in the field and discuss their physiological roles and their potential as drug targets.