Rheological properties were studied for aqueous solutions of poly(vinyl alcohol) containing sodium berate. The solution exhibited a marked shear thickening at a certain critical rate of shear, gamma(C) and the flow was unstable at higher rates of shear. The loss modulus exhibited a maximum and the angular frequency corresponding to the maximum, omega(max), was approximately equal to gamma(C). These features were common to several measurements including various molecular weights and concentrations of polymer and various temperatures. Possible mechanism of shear thickening was discussed based on a temporary network model composed of crosslink points of a finite lifetime.