To obtain the superhydrophobic water-repellent cotton fabrics, cotton fabrics were treated with silica nanoparticles and/or a cost-effective water-repellent agent (WR agent). Two different silica nanoparticles were synthesized via a sol–gel process and their shapes, sizes, and compositions were characterized. It was found that silica particles are spherical and have diameters of 143 and 378nm. For the cotton fabrics treated with the WR agent alone, the water contact angles on the fabric surface remained lower than 20° at the WR agent concentration of 0.3wt% or less. Silica nanoparticle treatment itself did not change the hydrophilic surface of cotton fabric, indicating that water drops were adsorbed into fabrics due to the hydroxyl groups on both cotton and silica nanoparticle surfaces. However, for the cotton fabrics treated with both silica nanoparticles and the WR agent, a contact angle above 130° can be obtained even at the very low WR agent concentration of 0.1wt%. Therefore, superhydrophobic cotton fabrics could be obtained via the combined treatment of silica nanoparticle and WR agent, which is cost effective compared with fluorinate silane treatment.