[en] The modification of mechanical properties of polyimide (PI) films by 2.0 MeV Si ions irradiation was investigated by means of Hysitron TriboIndenter In Situ Nanomechanical Test System (Hysitron TriboIndenter). The results indicate that the elastic modulus and the hardness have remarkable increase with the increase of the fluence. The elastic modulus of the modified PI at the fluence of 1.25 x 10¹⁵ ions/cm² is nearly five times that of the original PI, and the hardness of the modified PI at this fluence is more than 13 times that of the original PI. The friction coefficient changed from about 0.7 (original PI) to about 0.18 (modified PI at the fluence of 1.0 x 10¹⁵ ions/cm²). Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and Raman spectroscopy were applied to analyze the changes in the chemical structures