The microtubule (MT)-kinesin biomolecular motor system has attracted considerable attention due to its possible applications in artificial biomachines. Recently, an active self-organization (AcSO) method has been established to integrate MT filaments into highly organized assembled structures. The ring-shaped MT assembly, one of the structures derived from the AcSO of MTs, can convert the translational motion of MTs into rotational motion. Due to this attractive feature, the ring-shaped MT assembly appears to be a promising candidate for developing artificial devices and for future nanotechnological applications. In this work, we have investigated the effect of length and rigidity of the MT filaments on the size of the ring-shaped MT assembly in the AcSO process. We show that the size of the ring-shaped MT assembly can be controlled by tuning the length and rigidity of MT filaments employed in the AcSO. Longer and stiffer MT filaments led to larger ring-shaped assemblies through AcSO, whereas AcSO of shorter and less stiff MT filaments produced smaller ring-shaped assemblies. This work might be important for the development of biomolecular motor based artificial biomachines, especially where size control of ring-shaped MT assembly will play an important role.