The objective was to study the effect of pre-coagulation on removal of natural organic matter (NOM) and on fouling of membranes during ultrafiltration (UF). The influence of a coagulant type and the water pH on the process performance was analyzed. Two UF membranes (cut-off 30 kD) made of regenerated cellulose and polyethersulphone were used in the tests. Three aluminium-based coagulants - Al-2(SO4)(3), NaAlO2 and polyaluminium chloride (PAC) - were applied. The nature of the aluminium-based coagulant and solution pH strongly affected the performance of the coagulation/UF process. Under a given dose of aluminium the best results, i.e., the highest NOM elimination and the lowest permeate flux decline, were observed when alum or a prehydrolized coagulant were used.