Wastewater from an open stone cutting mine was ultrafiltered with a silica-modified alumina membrane (pore size 100 nm) and a gamma-alumina membrane (pore size 10 nm), in order to remove very fine suspended solids. For the 100 nm membrane the backflushing was used in all experiments to reduce cake layer formation during the filtration. For the 10 nm membrane the effect of backflushing was tested in one experiment. The permeate flux achieved with the 100 nm membrane decreased and continued to decline even after 24 h of filtration. This along with the high reductions of the pure water fluxes indicated the continuous fouling of the membrane. The rinsing of the membrane with the ion exchanged water and soaking of the membrane in diluted nitric acid between the filtration tests was not efficient enough to restore the pure water flux of the membrane. The permeate flux achieved with the 10 nm membrane was almost stable [55 l/(m(2)h)] and the fouling of the membrane was much smaller. Backflushing was not beneficial and a higher permeate flux was achieved without backflushing. The permeate quality achieved was similar to the water quality in the receiving lake.