The degradation of polypyrrole (PPy)-based films was examined in a 50% relative humidity and oxygen free atmosphere for 50 days. The results reveal that polymerization potential, modification of PPy with Cu(I), and treatment Of PPy with water in preparation, demonstrate significant influences on the conductivity and the corresponding stability of PPy. PPy prepared at an over-oxidizing potential and treated with water for 0.5 h exhibits a serious decrease in conductivity by about 93%, whereas the Cu-modified PPy becomes more stable. This is attributed to elects on transfer from Cu to the N+ of PPy. The concept of fixed and removable water adsorbed on PPy is introduced to explain the experimental results. Also, an aging mechanism involving the interaction between H2O and PPV is proposed to explain the decay in conductivity.