The temperature-dependent conductivity of polyaniline emeraldine salt (PAni-ES) was studied by terahertz (THz) time-domain spectroscopy from 80 to 290 K to investigate conduction properties in the THz region. The absorption coefficient and index of refraction increase with temperature. This reflects an increasing conductivity, which indicates a thermally assisted hopping transition. The frequency-dependent behavior of the conductivity is described by using the Mott-Davis model. The model fitting parameter, S, decreases with increasing temperature, indicating a possible correlated barrier hopping mechanism. Lastly, the activation energy at THz frequencies decreases with increasing frequency, suggesting intraband transitions. (C) 2014 Elsevier B.V. All rights reserved.