FGF-21 is a new member of FGF family and reported to regulate glucose metabolism, as well as lipid homeostasis, therefore, FGF-21 is a potential therapeutics for treatment of diabetes and metabolic syndrome. However, little is known about its functional receptor(s) and mechanism of action. The aim of the paper is to investigate the functional receptor(s) for FGF-21 in order to understand the mechanism of action of the molecule. Previous result showed that FGF-21 could stimulate glucose uptake in differentiated 3T3L1 adipocytes, but not in pre-adipocytes, suggesting that differentiated 3T3L1 adipocytes express functional receptor(s) for FGF-21. Therefore, the differentiated 3T3L1 adipocyte is a perfect target for searching receptor(s) of FGF-21. 3T3L1 pre-adipocytes were differentiated into adipocytes. The cell membrane of the life adipocytes were incubated with FGF-21 which was labeled with either Flag-tag or biotin, the FGF-21/receptor complexes were cross-linked once they interacted by cross-link reagent BS³. The FGF-21/receptor complexes were immunoprecipitated by either Flag antibody or streptavidin and analyzed by SDS-PAGE. The results showed that FGF-21 could form putative FGF-21/receptor(s) complexes with surface membrane protein of differentiated 3T3L1 adipocytes, not pre-adipocytes. The molecular mass of the complexes is proximate 300～400 ku. The complexes were formed by the FGF-21 labeled with either Flag-tag or biotin, suggesting the complex formation was not influenced by different labeling. To understand the component of the FGF-21/receptor(s) complexes, Western blot assay was used to examine the interaction of the complexes with known antibodies. FGFR-2 was detected within the FGF-21/receptor complexes by specific antibody for FGFR-2. To confirm the specific relationship between FGF-21 and FGFR-2, FGF-21-induced FGFR-2 tyrosine-phosphorylation was studied in 3T3L1 adipocytes. The results showed that although FGFR-2 was expressed in both pre-adipocytes and adipocytes FGF-21 could only enable adipocyte-expressed FGFR-2 tyrosine phosphorylation, which was consistent with glucose-uptake by FGF-21 in this two cell types. FGF-21 not only phosphorylated in situ adipocyte-expressed FGFR-2, but also ectopically expressed FGFR-2 in mouse pre-B cell line BaF3 cells. Sequencing analysis of FGFR-2 cDNA from adipocytes revealed that FGFR-2Ⅲc was the only subtype of FGFR-2 expressed in adipocytes, suggesting that FGFR-2Ⅲc is at least one of the functional receptors for FGF-21 and involved in glucose metabolism in the cells. In order to understand the reason why the same FGFR-2 only functions in adipocyte and not in pre-adipocytes, differential expression of FGFR-2 before and after 3T3L1 cell differentiation was systematically analyzed, the result showed that adipocytes expressed high level precursors of FGFR-2, which were not observed in pre-adipocytes, suggesting FGFR-2 turn-over rate could be a key factor to determine the function the molecule. Alternatively, adipocyte-specific molecules could be another key factor participating the signal transduction of FGF-21.