Amphipathic helices have been regarded as the basic lipid-associating domains of micellar complex formation. Apomyoglobin has still 27% α-helix at pH 4, and most of these helices are amphipathic. As the model system, the interaction between apomyoglobin and dimyristoylphosphatidylcholine (DMPC) is studied. At pH 4 and low lipid/protein molar ratio, the size decrease of DMPC vesicle is identified by light-scattering and Sepharose CL-4B column chromatography. The shape of vesicle-protein complex is observed to be changed from sphere to cigar form by electron-microscopic study. From the quenching test of tryptophan, it seems that N-terminal region of apomyoglobin is hydrophobically participated.