The performance of microfiltration of humic acid solution flocculated with PACl (polyaluminum chloride) was evaluated by the average specific cake resistance alpha(av) determined from the variation of the reciprocal filtration rate with the filtrate volume per unit membrane area. When PACl was added in excess to the solution at pH 5, alpha(av) increased remarkably due to the redispersion of flocs. On the basis of the results of the initial transmission of flocculated humic acid through the syringe filter, it was inferred that alpha(av) increased due to the increase in the quantity of submicron particles generated by the redispersion of flocs. This suggests that the measurements of the initial transmission by the syringe filter test may be utilized as a simplified method to test flocculation-microfiltration performance. Flocculation at pH 7 and the addition of bentonite to the solution improved the performance of microfiltration of humic acid solution flocculated with PACl by extending the range of PACl concentration in which flocs did not redisperse.