Polyelectrolytes are widely used to thicken hydrofracking fluids due to their good solubility and strong thickening power. However, their poor salt tolerance impedes their application at high salinity. To address this issue, a polyelectrolyte complex is prepared from anionic poly(acrylamide-co-acrylic acid-co-2-acrylamido-2-methyl-1-propanesulfonic acid) (PA3) and cationic homo poly((2-methacryloyloxyethyl) trimethyl ammonium chloride) (PDMC). While the viscosity of the PA3/PDMC complex initially decreases upon the addition of NaCl, it then increases at a higher NaCl dosage via the synergy of re-extended polymer coils and the cross-link structure between the oppositely charged counter ions. More significantly, this salt-induced viscosification leads to a high viscosity in a saturated oil-field brine, with a remarkable heat- and shear-resistance and proppant carrying capacity in comparison to the common HPAM-based system; moreover, the PA3/PDMC complex could be thoroughly broken within the allowed time and without residue. This oppositely charged polyelectrolyte complex may open a new pathway for polymer thickeners in high-salinity environments.