To provide a means for simply preparing an asymmetrical carbonic ester of high purity under a mild condition.

A method for separating a carbonic ester represented by general formula (I) from a mixture of the carbonic ester represented by general formula (I) and a carbonic ester represented by general formula (II) is provided. The method comprises obtaining a coagulum comprising the carbonic ester represented by general formula (I) by keeping the mixture at a temperature not higher than the freezing point of the carbonic ester represented by general formula (I) and higher than the freezing point of the carbonic ester represented by general formula (II) in the presence of an organic solvent, provided that the freezing point of the carbonic ester represented by general formula (I) is higher than that of the carbonic ester represented by general formula (II). In the formulae, R1 is an alkyl group, and R2 is an alkyl group other than R1.