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This paper proposes a single-phase, soft-switching, high step-up ac–dc converter based on a diode-capacitor voltage multiplier (DCVM) with a power factor correction (PFC). By applying the PFC technology, the proposed converter promises a near-unity power factor and a low distortion line current, while providing an adjustable, high step-up dc voltage that the conventional DCVM circuits cannot achieve. To reduce the switching losses, an auxiliary circuit for implementing a soft commutation is added to the power stage of the proposed converter. For operating at a fixed switching frequency, both the main and the auxiliary switches in the power stage are turned off with the zero-current transmission (ZCT). The operating principle, the design considerations and the control strategy of the proposed converter all are detailed and investigated in this paper. A 1.2 kV/500 W laboratory prototype, which employs a commercial PFC IC UC3854 as a controller, is built for test, measurement and evaluation. Under the full-load conditions, the measured power factor, the total harmonic distortion of the line current and the system efficiency are 99.6, 4.86 and 94%, respectively. The experimental results demonstrate the validity of the proposed converter.