Ceramic filters can be adapted to various liquids even under adverse conditions. Al2O3-based composites dispersed with 3 mol%-Y2O3-doped ZrO2 (3Y-ZrO2), or Al2O3/3Y-ZrO2, are well-known as extremely strong oxide-based ceramics. In this study, we have focused on the Al2O3/20 wt.% 3Y-ZrO2 composites as ceramic water filters. Disk-shape Al2O3/3Y-ZrO2 filters with different pore structures were prepared by pressureless sintering at 1200-1500 degrees C in air. The pore-size distribution of the filters was analyzed by mercury porosimetry. Some filtration properties, such as turbidity, were evaluated, and the Herman and Bredee's filtration models were discussed. Among the filters sintered at different temperatures, the Al2O3/3Y-ZrO2 filter sintered at 1300 degrees C showed the best performance due to the lack of large pores of > similar to 2 mu m. The average pore diameter of the A8Z2-1300 sample was 64 nm, the pore volume was 0.157 cm(3)/g, and the open porosity was 40.2%. SEM observations confirmed the change of the cake-layer thickness after the filtrations, i.e., similar to 27, similar to 17, similar to 15 and similar to 2 mu m for the A8Z2-1200, 1300, 1400 and 1500 samples, respectively, which revealed that the actual filtration in this study was the combination of (i) the standard blocking with the larger pores at the initial stage and (ii) the cake-filtration with the smaller pores at the middle and late stages.