Phototropins (phot1 and phot2) consist of two LOV domains (LOV1 and LOV2) in their N-terminus and a Ser/Thr kinase domain in their C-terminus. Although the photochemical properties of LOV domains have been extensively examined, their structural and functional roles remain to be determined. Here, we investigated the roles of phot2 N-terminus (P2N) in planta and in vitro. Size exclusion chromatography suggested that phot2 might exist in a multimeric form around 500 kDa in vivo, for which P2N but not P2C (phot2 C-terminus) is responsible. The multimeric formation was further confirmed by size exclusion chromatography using several recombinant proteins. The calculated molecular weights implied that P2N(1-533) and P2N(116-276) were probably tetramers but P2N(315-533) was a dimer, respectively. Physiological analysis of transgenic plants expressing phot2-deletion mutants insisted that the P2N(1-314) domain is dispensable to mediate the fundamental physiological responses. The functional relevance of the N-terminal domain of phot2 will be discussed.