1,2-Bis(2,4-octadecadienoyl)-sn-glycero-3-phosphocholine (DODPC), constructing the bilayer membrane of a vesicle, was polymerized by UV irradiation. The freeze-dried vesicles were completely dissolved in chloroform to obtain cross-linked phospholipid polymer (polyDODPC). The polyDODPC consisted of high molecular weight components and oligomers. The polyDODPC was dispersed by sonication, and two size distributions of the reconstituted vesicles were confirmed, larger vesicles from high molecular weight polyDODPC and smaller vesicles from oligomers. When the polyDODPC vesicles of various sizes and unimodal size distribution were reconstituted by an extrusion method, the vesicles of the same size as the vesicles at polymerization showed excellent stability compared with the other sizes. Interestingly, the original size of the polyDODPC vesicles could be completely restored by a cholate dialysis method. It was also clarified that vesicles larger than the original size were reconstituted from the higher molecular weight component, and the smaller vesicles were from the oligomers. Furthermore, a linear phospholipid polymer obtained from 1-palmitoyl-2-(2,4-octadecadienoyl)-sn-glycero-3-phosphocholine could not restore the original size. Those results indicate that the original size of the vesicles can be restored completely by all polyDODPCs having the original composition of large and small molecular weights and cross-linked structure.