To provide a microfibrillated rigid straight-chain aromatic synthetic polymer obtained by microfibrillating a pellet-like rigid straight-chain synthetic polymer and to provide a method for producing the polymer.

This method for producing the microfibrillated product of the rigid straight-chain comprises applying mechanical treatment in a water suspending state to the pellet-like rigid straight-chain aromatic synthetic polymer until the weight average fiber length of the polymer becomes ≤1.6 mm to carry out preliminary beating and then carrying out homogenizer treatment of the polymer.