Irradiation effect of the Al76Si4Mn20icosahedral quasicrystal (IQC) caused by 120 keV Ar ions and 1 MeV electrons has been studied by using transmission electron microscopy (TEM). The effect is dose and temperature dependent. At lower temperatures (≤345 K), Ar ions induces the Al-Si-Mn IQC fully amorphized. At medium temperature (352–400 K), only weak disordering and amorphization effects have been observed. At higher temperature (520∼670 K) no measurable effect has been observed by TEM. The temperature ranges are shifted to much lower temperatures for 1 MeV electron irradiation. The Ar ion and electron dual irradiation possesses the same effect as Ar ion irradiation. Heating the amorphized specimen to 600∼640 K induces it to transform to micro-quasicrystals and further heating to higher temperature (≥660 K) induces crystallization.