A full-bridge quasi-resonant DC-DC converter is provided, including a transformer having a primary winding and a secondary winding, a full-bridge converting circuit electrically connected with the primary winding of the transformer, a resonant capacitor provided between the full-bridge converting circuit and the primary winding, a rectifier circuit electrically connected with the secondary winding of the transformer, and a resonant inductor connected in series with the rectifier circuit. Therefore, the full-bridge quasi-resonant DC-DC converter reduces the switching losses of the switching elements and effectively reduces the size of the converter, while increases the conversion efficiency.