The influence of ionizing radiation on the physicochemical properties of panipenem in solid state was studied. In the first part of our studies, we evaluated the possibility of applying radiosterilization to obtain sterile panipenem. Spectroscopic (FT-IR, Raman), chromatography (HPLC and HPLC-MS) and X-ray powder diffraction (XRPD) studies have shown that irradiation of ertapenem with the 25 kGy, the dose required to achieve sterility, does not change the physicochemical properties of the studied compound. The antimicrobial activity of panipenem irradiated with the dose of 25 kGy was reduced for three species. It was confirmed that the decrease in antimicrobial activity might be related to isomerization of panipenem.