We used electrochemical impedance spectroscopy (EIS) to investigate microbial degradation of polyimides used as insulators in electronic packaging. The microbial inoculum was a fungal consortium isolated from degraded polyimides. Microorganisms grew on these polymers yielding distinctive EIS spectra indicative of failure. Degradation appeared to occur in a number of steps. Two distinctive stages in the decline of film resistance were observed in the inoculated EIS cells within 17 and 72 days after inoculation. The early stage of resistance decrease may be related to the ingress of water molecules and ionic species into the polymeric materials, whereas the second stage probably resulted from partial degradation of the polymers by fungal growth on the polymer film. The active fungal consortium was comprised of Aspergillus versicolor, Cladosporium cladosporioides, and a Chaetomium species. All of these fungi are common environmental contaminants. The relationship between changes of impedance spectra and microbial degradation of the coatings was supported by scanning electron microscopic observations of fungi on the surface of the inoculated polyimides. Our data indicate that the insulating polyimides used in electronic applications are susceptible to fungal degradation under appropriate environmental conditions, particularly in the presence of moisture.