The moisture and ethanol dependences of electrical properties of polyaniline (PANI) nanotubes doped with naphthalene sulfonic acid (NSA) are reported. The experiments were carried out in a temperature range from 80 to 300K. On the basis of analyzing the characteristics of the samples, we suggest that the resistance of the samples is dominated by the contact resistance between the PANI nanotubes, and the observed lnR(T)∝T-1/2 relation is explained in terms of the charge-energy-limited tunneling (CELT) model. The presence of water or ethanol molecules increases the conductivity, which is ascribed to the enhancement of charge carrier transfer and contact interface between the nanotubes upon exposure to water and ethanol. However, the extent of change during exposure to water and ethanol can be attributed to the differences in their chemical structures as well as their physicochemical properties.