The flocculating efficiency of some hydrophilic/hydrophobic cationic poly-electrolytes on montmorillonite suspension in water was investigated as a function of both the polycation structure and the flocculation parameters: polycation/montmoril-lonite contact time, suspension pH, polycation dose, and temperature. Cationic poly-electrolytes with quaternary ammonium salt groups in the backbone and hydrophobic side chains (hexyloxypropyl, PCA₅H₁ and PCA₅H₂; and decyloxypropyl, PCA₅D₁, respectively) were used as flocculants. The flocculation was time dependent. A negative influence of the stirring time and of the abrupt variation of pH from basic to acidic on the separation efficiency was evidenced. The increase of the polycation dose from 0.58 mg polycation/g montmorillonite up to 1.74 mg/g montmorillonite showed a positive influence on the sedimentation of montmorillonite particles for all the polycations taken into account. The influence of the polycation structure was reflected in the lower turbidity found in the case of the polycation PCA₅D₁ compared with that of PCA₅H₁, at the same concentration; this reflects the positive influence of the hydrophobicity increase on the suspension separation. A common characteristic for all the polycations is that, for more than about 60 min of settling, the lowest turbidity was found at 25°C and the highest at 5°C. The turbidity found at 15°C was in between, both before and after 60 min of settling time.