Glass fragments are valuable evidence in the criminal investigation of hit-and-run, murder and burglary cases. Screening of glass fragments should be carried out by refractive index (RI) measurement after the identification of unknown fragments of glass by analysis using electron probe microanalysis (EPMA), scanning electron microscopy with an energy dispersive X-ray spectrometer (SEM-EDS) and/or X-ray fluorescence spectrometry (XRF). However, it has been pointed out that RI values of glass fragments can be influenced by electron beam and/or X-ray of the instrumental analysis, although the effect of them on RI values of glass has not been sufficiently examined.   In this work, we compared the RI values of glass fragments before and after irradiation by electron beam and/or X-ray using these devices. Glass fragments were collected from 3 different uses (windowpane of building, windshield and beer bottle). No significant difference was recognized in the RI values of these glass fragments before and after 30 minutes of irradiation.   We have ascertained that the effect of electron beam and/or X-ray on the RI values is negligible in the conditions of the present study and that comparison of RI values is still useful for the forensic screening of glass fragments even after the instrumental analysis described above.