An improved process for preparing a diaryl carbonate from a diaryl oxalate in a liquid phase by decarbonylation utilizes a reaction vessel composed of two or more reaction chambers which are connected in series. The process is composed of the steps of continuously introducing the diaryl oxalate and an organic phosphorus compound having a trivalent or pentavalent phosphorus atom and at least one carbon-phosphorus bonding into the first chamber and continuously recovering a reaction mixture mainly containing the diaryl carbonate from the last chamber under the condition that a mixture of the diaryl oxalate and the organic phosphorus compound is heated in the reaction chambers, while discharging carbon monoxide released from the mixture.