Poly(lactic acid) (PLA) is a biodegradable polymer which has one of the highest consumption volumes in the world. Due to its specific properties, especially those that make it ecologically acceptable, it has a wide application from food packaging to medical implants. In this work, commercially available 3D-printing filaments of PLA were used. The objective of this study was to investigate the effects that exposure to -radiation has on this polymer. The study of structural changes in polymers due to ionizing radiation is crucial since this radiation treatment is often used as a method for sterilization of food packaging and medical implants, but also as a simulation of the conditions in space or in particle accelerators. The samples were irradiated with total absorbed doses of 25 kGy, 50 kGy, 100 kGy, 200 kGy and 300 kGy. The experimental techniques used to investigate the structural changes in PLA filaments were electron paramagnetic (spin) resonance (EPR or ESR), Fourier transform infrared (FTIR) spectroscopy, compressive strength test and differential scanning calorimetry (DSC). EPR was used to monitor the formation and stability of free radicals formed due to ionizing radiation. The radical concentration is dependent on the applied irradiation dose, while the spectral lineshape appears to be dose independent. The loss of the ESR signal, directly related to the decrease of radical concentration, was monitored as a function of time for all applied radiation doses. ESR results were supported by those observed by other methods. FTIR spectroscopy was used to record the vibrational spectra of the samples in order to observe eventual appearance and/or disappearance of some chemical bonds. Although the intensity of the spectral bands is dose dependent, the shape of the bands did not change due to irradiation. This result differs those found in the literature. A compressive strength test was performed to study the changes in mechanical properties of PLA. The force-at-break and the Young modulus were the parameters of interest. They were hard to compare with previous work since the compressive strength test is rarely performed due to its geometrical losses. In our case this type of test was the last resort because the samples could not be straighten up for a tensile strength test, due to their fragility. 1 An extremely important information on the effects of -radiation on PLA was a shift of the glass transition temperature as a function of radiation dose, investigated by DSC. The results were supported by those obtained by other methods.