In this study, flat-tubular-type alumina filters were manufactured using alumina powder of two sizes ($2.4{mu}m$ ALM-44 and $0.4{mu}m$ AP 400) by an extrusion process. The manufactured alumina filter was sintered at $1200-1600^{circ}C$ for 1 h. As particle size increased, the largest pore size, average pore size and porosity increased; but density and linear shrinkage decreased. The alumina filter fabricated using ALM-44 powder sintered at $1500^{circ}C$ was confirmed as the best water treatment filter after investigation of the bending strength, water permeability and impurity-removal efficiency of the experimental filters. This flat-tubular-type alumina filter is expected to be useful not only for direct water treatment, but also for use as a support filter during coating processes, to control pore size.