The dielectric and biological properties of chitosan (CTS)-based nanocomposites were analyzed by dielectric spectroscopy, and antibacterial and antifungal assays. Carbon nanotubes (CNT) and CNT decorated with silver nanoparticles (AgnP) were incorporated into a CTS matrix at different concentrations to obtain bionanocomposite thin films. The conductivity of pristine CTS is considerably enhanced, by six orders of magnitude, with the inclusion of CNT; however, with the addition of CNT decorated with AgnP it only increases by two orders of magnitude because of strong chemical interactions between the CNT and AgnP that also affect the antibacterial activity of the composite. The percolation threshold in the CTS/CNT composites is ca. 1.3 wt %, while in CTS/CNT-AgnP composites the strong CNT-AgnP chemical interactions give a percolation threshold of ca. 2.2 wt % of CNT-AgnP. In both cases, DC conductivity exhibits a three-dimensional hopping conductivity, and the σ- and α-relaxation processes are disclosed in agreement with the pristine CTS relaxation processes previously reported; however, these two relaxations vanish in the vicinity of the saturation concentration. Finally, the antifungal activity of the CTS/CNT-AgnP composites is comparable with the activity of other composites, while their antibacterial activity seems to be competitive with respect to commercial antibiotics, indicating the effectiveness of these composites in potential hygienic applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40214.