The micro-two-phase sheath flow/fluorescence microscopy was used for the fluorescence lifetime measurement for the first time. An inner micro-flow of the toluene solution of samarium(III) complex was flowed in an aqueous phase stream. From the fluorescence decay images observed in the inner flow just after the excitation point, the fluorescence lifetime of the complex was observed. By flowing a toluene solution of ligands into the Sm(III) aqueous stream, the interfacial formation of the fluorescent complex was observed.