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The thermal aging of conducting polypyrrole/polyaniline (PPy/PA) blends heated at 70°C for up to about 600 hours was studied by d.c. conductivity measurements and by thermally stimulated depolarization current (TSDC) spectroscopy in the temperature range from 80 to 300 K. The composition of the samples varied from pure polypyrrole to pure polyaniline with the PA content increasing in steps of 10%. Although the σ = σ(T) curves seem smooth, the corresponding Δσ/ΔT = f(T) curves exhibit systematically ascattering of points in the temperature ranges from 100 to 140 K and from 225 to 320 K approximately for all the samples before and after the heat treatment. TSDC measurements with the MISIM (metal-insulator-sample-insulator-metal) configuration, show a low temperature peak at 100–120 K and a high temperature peak at 280–300 K. The first disappears when the polypyrrole content exceeds 70% and for all the samples after heat treatment, although the high-temperature peak persists. The explanation given to this correspondence between d.c. conductivity and TSDC signals is based on the destruction of conformons and the mobility change of the polymer chains with rising temperature.