Abstract: Method of manufacturing a radially corrugated expander-spacer for a piston oil ring assembly, having inner and outer crowns alternately and successively laid, which can prevent its both terminal ends from nesting together during assembling of the piston oil ring assembly. The inner crowns each includes an inner peripheral piece and an opening having a circumferential width larger than that of the inner peripheral piece, and the outer crowns each includes an outer peripheral piece and an opening having a circumferential width larger than that of the outer peripheral piece. The manufacturing method comprises the steps of filling thermosetting synthetic resin having bonding force with respect to metals into the openings of inner crowns at both terminal ends of the expander-spacer, and thereafter, setting the thus filled thermosetting synthetic resin so that the resin is fixedly secured to the openings of the inner crowns at both terminal ends of the expander-spacer.