The present invention relates to a method for isolating pluripotent/multipotent stem cells derived from umbilical cord blood, characterized by culturing mononuclear cells isolated from umbilical cord blood in a culture vessel containing fibronectin and then harvesting stem cells from the culture, the umbilical cord blood-derived pluripotent/multipotent stem cells isolated thereby; and a cell therapeutic agent containing the pluripotent/multipotent stem cells derived from umbilical cord blood or cells differentiated therefrom. The present invention also relates to a novel culture media for stem cells, a culture method for stem cells which is characterized by culturing and proliferating stem cells in the culture media, and a method for increasing sternness of stem cells which is characterized by a sphere culture or a three-dimensional culture of stem cells.