Disclosed is a process for producing an oxazoline derivative from a non-protected sugar in a simple manner. Also disclosed is a process for producing a glycoside by utilizing the product of the aforementioned process. A sugar oxazoline derivative is synthesized in one step in an aqueous solution from a sugar having a free hemiacetalic hydroxy group and an amido group by using a haloformamidinium derivative as a dehydrating agent. A glycoside compound is produced by using the oxazoline derivative as a sugar donor and also using a sugar dehydrogenase. The method can be applied to the production of a compound having a long sugar chain, and is therefore useful for the production of a physiologically active oligosaccharide, a carrier for a drug delivery system, a surfactant, a carbohydrate-based drug, a glycopeptide, a glycoprotein, a carbohydrate polymer or the like.