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The effects of 400 keV helium ion irradiation dose and temperature on the microstructure of the Ti3SiC2 ceramic were systematically investigated by grazing incidence x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The helium irradiation experiments were performed at both room temperature (RT) and 500℃ with a fluence up to 2.0 × 1017 He+/cm2 that resulted in a maximum damage of 9.6 displacements per atom. Our results demonstrate that He irradiations produce a large number of nanometer defects in Ti3SiC2 lattice and then cause the dissociation of Ti3SiC2 to TiC nano-grains with the increasing He fluence. Irradiation induced cell volume swelling of Ti3SiC2 at RT is slightly higher than that at 500 ℃, suggesting that Ti3SiC2 is more suitable for use in a high temperature environment. The temperature dependence of cell parameter evolution and the aggregation of He bubbles in Ti3SiC2 are different from those in Ti3AlC2. The formation of defects and He bubbles at the projected depth would induce the degradation of mechanical performance.