In this paper, a new series input parallel output (SIPO) interleaved flyback converter is proposed. Since voltage stresses on all semiconductor devices in primary side are clamped to input voltage, the proposed converter shows low conduction and switching losses. Secondly, since the proposed converter has regeneration of the leakage inductance energy, it shows high efficiency compared to conventional flyback converter. Furthermore, because of its simple structure, the proposed converter can have maximized power density. The feasibility of the proposed converter was verified by experimental results with a prototype of 240W, 330–400V input, and 24V output. The proposed converter shows high efficiency, more than 90% in the entire load condition.