This study investigated the steady shear viscosity η and the oscillatory complex viscosity η * of poly(p-phenylene terephthalamide) solutions in sulfuric acid (PPTA/H 2 SO 4 ) by rheometric measurements. The influences of steady shear rate, concentration, and temperature were investigated in detail. The results indicated that in the plateau regime (η independent of γ : regime), η shows a non-monotonic variation with the concentration increase, which reaches the maximum value when the solution changes from the isotropic phase into the nematic-isotropic biphasic system. At the low shear rate, the corresponding critical concentration C * η is close to the critical concentration C * , at which the birefringence emerges in solutions. In the plateau regime, the dependence of η on temperature follows different rules when the system is in different phases. In the isotropic phase, η decreases with the increasing temperature and obeys the Arrhenius exponential rule. Unlike the isotropic solution, η increases with the temperature in the nematic-isotropic biphasic region and decreases linearly with the temperature in the nematic phase region. The η * measured at different angular frequencies (ω) was compared with η measured at different γ : . For the isotropic solutions, the |η * |~ω curve coincides with the η~γ : variation in a wide shear rate range for the plateau regime, while in the nematic phase region, |η * | is always smaller than η. For the biphasic systems, the consistency can be seen only in a narrow shear rate range and |η * | deviates from η with the increasing shear rate.