The effect of fluid force on detergency has been experimentally investigated. More than one hundred wires of 50 μm in diameter, as a model of two dimensional soil, were set so as to adhere to a bottom flat plate of a two dimensional channel. The aqueous solution of surfactant and the dilute aqueous solution of polymer were made to flow through the channel and the pressure drop caused by the wires was measured. The drag and the drag coefficient (CD) of one wire were estimated with the pressure drop by the use of the law of momentum. The following results are obtained. For all solutions used, the drag increases and the drag coefficient decreases with an increase in the Reynolds number based on the wire diameter taken as the characteristic reference length. The solution of LAS, one of familiar anionic surfactants, givesCDvalues lower than the pure water, and the difference becomes marked as the concentration of the solution increases. A nonionic surfactant solution, AE 1.0%, shows a time dependent character; it provides about half of the correspondingCDvalue of water within a day since the solution was produced, while it gives nearly the same as that of water after 4 days have passed. TheCDfor dilute solution of polymer (PEO 20 ppm) in water is higher than those for water and surfactant solutions. Viscosities of the solutions tested were Newtonian and the magnitudes are in the same order for all three solutions. These results suggest that the variation ofCDobserved for the three solutions is not directly related to the solution viscosity but probably to other properties such as elastic force.