A self-powered flyback pulse resonant circuit (FPRC) is proposed to extract energy from piezoelectric (PEG) and thermoelectric generators (TEG) simultaneously. The FPRC is able to cold start with the PEG voltage regardless of the TEG voltage, which means the TEG energy is extracted without additional cost. The measurements show that the FPRC can output 102 µW power under the input PEG and TEG voltages of 2.5 V and 0.5 V, respectively. The extracted power is increased by 57.6% compared to the case without TEGs. Additionally, the power improvement with respect to an ideal full-wave bridge rectifier is 2.71× with an efficiency of 53.9%.