A medical material for in vivo implantation use, characterized in that a polyethylene terephthalate ultrafine fiber is provided in at least a part of the medical material, wherein the polyethylene terephthalate ultrafine fiber is produced by spinning a polyethylene terephthalate chip, which is produced using germanium or titanium oxide as a catalyst, by a direct spinning method and then stretching the spun product and has a single fiber fineness of 0.8dtex or less.