PURPOSE: To obtain a predispersion of staple fibers useful as a reinforcing material by uniformly dispersing fibers without cutting the fibers.

CONSTITUTION: This predispersion of staple fibers comprises a formed mixture of staple fibers dispersed by suspending and fluidizing thereof using a circulating gas stream with powder or a binder solution. Furthermore, the method for producing the predispersion of the staple fibers is to introduce a gas from a gas introduction port 2 provided in the central part in the upper part of a container 1 into the container 1, suspend and fluidize the fibers and powder respectively charged from a fiber charging inlet 3 and a powder charging inlet 4 into the container 1 with the circulating gas stream in the vertical directions, mix both, produce the circulating gas stream, descending in the vertical direction of the container and rising along the inner wall of the container. In the method, the fibers may previously be suspended, fluidized, opened, then suspended and fluidized together with the powder. The container 1 is equipped with vent holes 6 having a filter 7 so as to regulate the discharge of the fibers and powder. The opened fibers may then be brought into contact with the binder solution such as an aqueous solution of sodium carboxymethyl cellulose to subsequently form the resultant dispersion.