Heretofore, as a method for preparing an N,N′-dialkoxy-N,N′-dialkyl oxamide, there has been disclosed a process in which oxalyl chloride and N,O-dimethylhydroxylamine hydrochloride are reacted in the presence of pyridine to prepare N,N′-dimethoxy-N,N′-dimethyl oxamide (for example, see J. Org. Chem., 60, 5016 (1995)). In this method, however, there are problems that phosgene having high toxicity and oxalyl chloride which is likely decomposed to carbon monoxide are used as starting materials, and yet methylene chloride having high carcinogenic properties must be used in an isolating operation of the objective product, so that it was not suitable for an industrial process for preparing an N,N′-dialkoxy-N,N′-dialkyl oxamide.