The complexation of poly(vinyl alcohol) (PVA) with congo red (CR) ions in aqueous solutions was investigated as functions of PVA (C(PVA)) and congo red concentrations (C(CR)) and temperature. The PVA-CR complexation resulted in a gelation around pH 7 when both C(PVA) and C(CR) were high enough. However, in the case of intermediate PVA concentrations in monomer unit, i.e., 0.6 mol/L, a sol-gel-sol-gel-type transition was observed with increasing CR concentration. The origin of this "re-entrant"-type phase transition was studied by estimation of the enthalpy of cross-link formation and by capillary viscometry. The gelation was classified into two steps : (a) weak cross-link and (b) strong cross-link formations. These mechanisms were characterized by the value of the enthalpy of cross-link, DELTAH. The former is in the order of -5 kcal/mol and the latter -20 kcal/mol. This viscosity behaviors in a dilute polymer concentration regime were also classified into several regions : When both C(CR) and C(PVA) were low, the complex solution showed a typical viscosity behavior for a polyelectrolyte solution. With increasing C(CR) and C(PVA), there appeared a region where a time-dependent viscosity thickening took place. With further increase in C(PVA), the viscosity recovery a behaviors similar to that for a PVA solution without CR. The connection between these rheological properties and sol-gel transition is discussed by taking into account the ionic screening effect and complexation equilibria.