To provide a method for preparing a polymer slurry that prevents spreading of the polymer particle diameter distribution caused by distribution of the shearing force inside a device.

The method for preparing a polymer slurry comprises using a rotary mixer provided with an inlet for a polymer slurry comprising an organic solvent solution in which a polymer is dissolved (heretofore referred to as polymer solution) and an inlet for the poor solvent at the upper part of the mixer and a rotor with a pin at the lower part thereof, feeding the polymer solution from a side of the mixer and the poor solvent from the upper surface thereof, and bringing the polymer solution and the poor solvent into uniform contact with each other by the use of the pin disposed at the rotor that is driven by a motor, in a method for obtaining the polymer slurry comprising bringing the polymer solution into contact with a poor solvent that does not dissolve the polymer but dissolves the solvent under shearing force.