The effect of pH on the flow behavior of ZrO2 suspensions containing polyacrylic and octanoic acids was evaluated. In the flocculated pH regime, the flow behavior is highly shearthinning and can be described by a power-law model. The shearthinning behavior increases with increasing degree of flocculation. Maximum shearthinning was observed at the zero zeta potential condition. Hydrophobic interaction arising from adsorbed octanoic acid was found to enhance the shearthinning behavior. No such enhancement was observed for adsorbed polyacrylic acid. It was also illustrated that the viscosity-pH behavior is a mirror image of the yield stress-pH behavior. A quantitative particle-pair interactions model incorporating steric and hydrophobic interactions was proposed to explain the effects of polyacrylic and octanoic acids on the maximum yield stress.