Interstitial strengthening is one of the main approaches to improving the mechanical properties of high-entropy alloys (HEAs), but its effects on the irradiation resistance of HEAs need further study. Here, we investigated the irradiation-induced defects and swelling of Fe38Mn40Ni11Al4Cr7HEAs with different carbon contents under 5 MeV Xe(23+)irradiation at 300 degrees C and 500 degrees C. Results show that the irradiation-induced swelling was significantly suppressed as the carbon content increased. Under the observation of TEM, the size of irradiation-induced dislocation loops also decreases with increasing carbon content. By comparing the effects of carbon content at different temperatures on the evolution of defects, the pinning effect of interstitial carbon on irradiation-induced defects of HEAs was proposed and analyzed. Carbon atoms, which are stabilized in the octahedron clearance of HEAs with FCC structure, not only promote the recombination of point defects by enhancing the sluggish diffusion effect of HEAs, but also pin the common 1/3 <111> faulted loops caused by irradiation. This pinning effect is the main mechanism of interstitial carbon for improving the irradiation resistance of HEAs below 300 degrees C. In summary, this study provides an essential experimental basis for the irradiation effects of carbon-doped HEAs and strives to reveal the effect of interstitial carbon on irradiation-induced defects at different temperatures. [GRAPHICS] .