A new and efficient Ionic Liquid-Supported Oligosaccharide Synthesis (ILSOS) strategy for an N-linked core pentasaccharide on a 10 g scale is reported. This new ILSOS includes a new spacer for an IL support, a new tagging strategy, and fast, efficient and orthogonal removal of the ionic-liquid support, producing the N-linked core pentasaccharide with direct applicability potential in a short time, with high yield and on a large gram scale.