The present invention relates to a novel method of purifying adefovir dipivoxil of Formula 1. The purification method according to the present invention comprises the steps of dissolving impure adefovir dipivoxil containing byproducts generated during a synthetic reaction, salts thereof or complexes thereof in water or a water-containing mixed solvent; purifying the adefovir dipivoxil solution through a reverse-phase column; and adding a base to the purified adefovir dipivoxil solution and extracting the same with an organic solvent.
Further, the present invention provides a method of preparing amorphous adefovir dipivoxil by removing the solvent from the high purity solution of adefovir dipivoxil represented by formula I purified by the above method.