A microwave cavity method was used to measure the electron density in the afterglow period of a pulsed dc glow discharge. The measurements were carried out in the mixture neon with 6 × 10−2% of helium for the pressure interval from about 5 to 25 torr.The de-excitation cross section of metastable atoms was found to be 1·09 × 10−19 cm2. It was also found that the late afterglow period is affected only by the ambipolar diffusion of ions and electrons at all measured gas pressures.The value of an effective reduced mobility coefficient was calculated from the measured value of the ambipolar diffusion coefficient and it was found to be 8·37 ± 0·84 cm2V−1 s−1. This value is in a good agreement with the theoretical value calculated according to the Langevin formula for molecular (NeHe)+ ions in neon. It is supposed that these ions strongly affect loss processes of electrons in this mixture during the afterglow period.