The long-lived -radionuclidic impurities in the columns of spent99Mo/99mTc generators one year after the calibration date have been determined by -spectrometry. Three radionuclidic impuritiesfission products (103Ru,106Ru and125Sb) were detected. Also in the majority of samples three radioisotopes of tungsten (181W,185W and188W) were also present. The contents of the impurities were found to vary greatly. According to the activity, energy and half-life, the main contribution to the residual activity in the spent generators is due to the presence of125Sb.