The dependence of the intrinsic viscosity of a number of aromatic polyamides and poly-p-phenylene oxadiazole in sulphuric acid on temperature has been investigated. Characteristic of all the polyamides is a high negative value of the temperature viscosity coefficient which is interpreted as the result of increase in equilibrium flexibility due to deformation of the amide groups during thermal motion. It is shown that the temperature viscosity coefficient rises with increase in the MW of the polymers studied.