Sharp changes in the transport and structural properties were noticed when a pH-dependent study of polyaniline (PAN) with monovalent (Cl-) and multivalent (PO4)(3-) ions was carried out. Scanning electron micrographs (SEM) of these samples reveal that the sharp changes induced by doping are more prominent at the pH where the transformation of the PAN lattice takes place. A channel formation has been observed at a pH of 3.0 in the case of HCl and 2.5 in the case of H3PO4 doping, with flattening of the structure. The d.c. conductivity of the samples in this pH range has been measured in the temperature range 77-300K. The d.c. conductivity data have been analysed in the light of existing theoretical models. Mott’s 3D variable range hopping (VRH) is the mechanism responsible for charge transport at low temperatures for HCl as well as H3PO4 doped samples, whereas a deviation is observed at higher temperatures for all the HCl doped samples. However, lightly doped H3PO4 samples give a T-1/4 dependence. At a moderate doping level (pH 2.5), a deviation from 3D VRH is observed at higher temperatures, indicating thereby a temperature and composition dependent charge transport. A lesser conductivity is obtained in the case of H3PO4 doping in comparison to HCl for the same pH value, which may be due to cross-linking induced by the multivalent ion.