Abstract Only scant and conflicting information is available in the literature on the effect of temperature on flocculation. In the present work an attempt was made to determine the effect of temperature on zeta potential, the rate of flocculation, and the optimum pH and dosage of flocculant. Cell electrophoresis and light absorption techniques were used in flocculation experiments. Bentonite and kaolinite clays dispersed in distilled water were chosen as dispersion systems. Alum and three polyelectrolytes (cationic, anionic and non-ionic) were used as flocculants. The temperature range investigated was 1°–20°C. The results indicate that: 1. 1. Temperature has no significant effect on the zeta potential of a clay particle dispersed in water. This is in agreement with the theoretical prediction of the Poisson-Boltzman equation. 2. 2. Charge neutralization is an important factor in the flocculation of charged clay dispersion. However, the degree of charge neutralization necessary for effective flocculation depends strongly on the nature of the clay used. 3. 3. There is some correlation between zeta potential and flocculation. In the case of alum, for example, zeta potential may be used as a criterion of flocculation. 4. 4. The optimum pH for a given degree of flocculation varies with temperature when alum is used as flocculant. However, when flocculation is carried out at optimum pH conditions temperature has no effect. This supports the kinetic equations of Smoluchowski. 5. 5. When cationic polyelectrolytes are used for flocculation of aqueous dispersion, the rate of flocculation, the optimum pH, and the flocculant dosage required to achieve a given degree of flocculation are independent of temperature. This is interesting from a practical point of view, for example when the substitution of alum with a cationic polyelectrolyte flocculant is considered in a water treatment facility.