In order to correlate rheological and filtration parameters of clay-aqueous suspensions, the effect of acidic pH and ionic strength have been investigated. Two clays, a bentonite and a palygorskite were used to emphasize the contribution of the nature of the clay. Rheological results show that at a given bentonite percentage, when the pH of the suspension decreases, the yield stress and dynamic viscosity increase and reach a maximum at weakly acidic media before decreasing again in highly acidic medium where the structure of the clay is probably attacked. The NaCl addition to palygorskite suspensions causes an abrupt increase in viscosity at the critical flocculation concentration (CFC) revealing the beginning of the flocculation. When the ionic strength increases further, the viscosity reaches a maximumthen decreases when the suspension becomes unstable. The effect of the pH on the filtration properties for the bentonite appears to be the same as on the rheological properties. When the pH decreases, the thickness (e), the weight (m) and the water retention (WR) of the cake increase, reach a maximum for weakly acidic pH before decreasing again. The permeability of the cake increases below the pH corresponding to the observedmaximumfor the other filtration parameters.However, the addition of NaCl and the flocculation phenomenon seem to have no effect on the filtration properties of the palygorskite. There is no correlation between rheological and filtration parameters for the non swelling and fibrous clay.