When ethylene, containing a small amount of gaseous alcohol, was irradiated by gamma rays, the G(- C2H4) had a maximum value at the addition of ethyl, isopropyl or t-butyl alcohol less than 0.03 electron fraction. The total concentration of mixtures was 1.1 × 10−4mole/cc. On the other hand, the appearance potential of negative ions, formed by dissociative-resonance-electron-capture processes of slow-electron impact, was measured by mass spectrometer. The lowest value for ethanol (2.7 eV) was much lower than that for ethylene (7.9 eV). This fact suggests that slow electrons in the system are more or less captured by alcohols added to retard the neutralization of positive ethylene ions. The enhancement of the ethylene consumption by adding alcohols is, therefore, attributed to the ion-molecule reactions, that is, the ionic polymerization of ethylene.