The paper proposes a Marx topology DC-DC boost converter (MTBC) with a high boot ratio, where a parallel connection is applied on the input side in order to reduce the conduction and copper losses while a series connection is applied on the output side in order to reduce the voltage stress on switching devices. With the proposed circuit configuration, the high boost ratio DC-DC converter achieves high efficiency. A three-stage MTBC with a boost ratio of 8.33 between the input and output voltages was designed and constructed. A maximum efficiency of 94.5% was achieved with the designed three-stage MTBC. The loss analysis showed that the iron and conduction losses were dominant. The volume analysis showed that the proposed three-stage MTBC requires approximately 23% less of a total volume compared to the conventional isolated DC-DC converter with a two-series-output-rectifier (ICSR) while reducing the power loss of semiconductor devices.