The irradiation stability of a material in the temperature range from 300°C to 500°C represents an important step for a variety of nuclear applications. Here we used dual-beam irradiation to investigate the response of an amorphous silicon oxycarbide (SiOC) to extreme environments (temperature and irradiation). The amorphous SiOC was prepared in thin film form by sputtering and then fabricated into cross-sectional transmission electron microscopy (TEM) specimens, and finally irradiated with helium (He) and krypton (Kr) ions inside a TEM. In-situ TEM observations revealed that He bubble and void formation are highly suppressed after irradiation up to 95 dpa with simultaneous He implantation up to 231 at.%. Atomic pair-distribution functions suggested that the amorphous structures are almost the same before and after irradiation, and no crystallization, nor phase separation was detected. This study demonstrates the stability of amorphous SiOC under dual-beam irradiation at nuclear reactor operation temperatures, suggesting that this material is applicable as a structural material for advanced nuclear reactors.