A modified ZVT SEPIC-Boost DC-DC converter is proposed in this paper. The converter has good characteristics such as; high-voltage gain, continuous input current with low ripple, ZVT condition for all switches in a wide power range operation, and low voltage stress for diodes. Moreover, the converter has high efficiency due to soft switching condition for all semiconductor devices. Besides, the control circuit is simple and remains PWM. The proposed converter has been compared with other similar structures from different aspects, which shows its superior performance. Principles of operation and design procedure for components are presented in details. A 200 W laboratory prototype of the converter with 40 V input voltage and 400 V output voltage under 100 kHz switching frequency is implemented and experimental results confirm the theoretical analysis and indicate efficiency of 95.2%.