This paper presents a high-efficiency and high-step-up nonisolated interleaved dc–dc converter with a common active-clamp circuit. In the proposed converter, the coupled-inductor boost converters are interleaved. A boost converter is used to clamp the voltage stresses of all the switches in the interleaved converters, caused by the leakage inductances present in the practical coupled inductors, to a low voltage level. The leakage energies of the interleaved converters are collected in a clamp capacitor and recycled to the output by the clamp boost converter. A new topologies and interleaving modulation concepts for multilevel dc–dc boost converter enabling a significantly less loss and a reduced chip size of the power semiconductors are proposed. The proposed converter achieves high efficiency because of the recycling of the leakage energies, reduction of the switch voltage stress, mitigation of the output diode’s reverse recovery problem, and interleaving of the converters. A prototype of the proposed converter is developed, and its experimental results are presented for validation.