Vesicle fusion plays an important role in molecular transport and signal transduction in vivo. Fusion occurs even in artificial vesicles without proteins, as long as cations are present similar to the physiological environment. The progress of fusion between vesicles encapsulating a fluorescent dye (calcein) and giant unilamellar vesicles (GUVs) was examined using a fluorescence microscope. In the case of vesicles formed with phosphatidylcholine (PC) alone, the fusion begins upon the suppression of electrostatic repulsion by cations such as Ca2+. However, almost all vesicles remain in the state of adsorption or hemifusion even after 1 h or more, and it is difficult to proceed to full fusion. In contrast, mixing phosphatidylethanolamine (PE) with vesicles facilitates the progression from hemifusion to full fusion, and the transfer of calcein to the GUV was observed immediately after beginning the vesicle fusion. This is probably because the small head group makes the fluid phase lipid bilayer unstable.