A method for producing an oxazoline derivative from a non-protected sugar in a simple manner and a method for producing a glycoside by utilizing the product of the aforementioned method are disclosed. A sugar oxazoline derivative is synthesized in one step in an aqueous solution from a sugar having a free hemiacetal hydroxy group and an amide group by using a haloformamidinium derivative as a dehydration/condensation agent. A glycoside is produced by using the oxazolidine 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 a production of a physiologically active oligosaccharide, a carrier for a drug delivery system, a surfactant, a carbohydrate pharmaceutical, a glycopeptide, a glycoprotein, a carbohydrate polymer or the like.