In the present work, the influence of electron-beam irradiation on thermo-mechanical properties of HDPE and HDPE/Sugarcane bagasse fiber composite was investigated. The materials were irradiated using a Dynamitron electron beam accelerator, at room temperature in presence of air, at radiation dose 100 kGy, at dose rate of 28.02 kGy/s. Irradiated and non-irradiated samples were submitted to thermo-mechanical tests and the correlation between their properties was discussed. The results showed significant (p < 0.05) changes in thermo-mechanical properties of HDPE, due to sugarcane bagasse fiber incorporation, except to tensile strength at break and Vicat tests. In addition, for both, HDPE and HDPE/Sugarcane bagasse fiber composite, the electron-beam irradiation promoted a significant gain up to 200 % in tensile strength at break, flexural strength and flexural modulus and promoted a significant decrease only at elongation at break of the irradiated HDPE/Sugarcane bagasse fiber composite.