[en] The nuclear powered ship 'Otto Hahn' was commissioned in 1968, and ended its mission in 1979. The decommissioning was approved in December, 1980, and after the dismantling and removal of the reactor plant were completed, the decommissioning was recognized in September, 1982. The features of the method of decommissioning Otto Hahn were the carrying-out of the reactor pressure vessel together with the primary shielding tank as one body, and after the machinery, equipment and structures in the controlled area were removed or decontaminated, the ship was reconstructed to a diesel freighter. It is considered that the method of decommissioning of Otto Hahn and the data obtained by this work furnish much information for the decommissioning of nuclear power stations and nuclear powered ships hereafter. In this report, the course of decommissioning of Otto Hahn and its experience are synthetically summarized. The propulsion plant of Otto Hahn, the radiological condition, the conceptual design of decommissioning, the dismantling works, the procedures of permission and approval, the procedure for removing the control, the execution of decommissioning, and the removal of the controlled area are reported. (K.I.)