It has been shown that stable aqueous dispersions of nanoparticles of the rigid-rod ladder-type polymer poly(benzo-bisimidazobenzo-phenanthroline) (BBL) can be prepared in order to facilitate BBL processing. The obtained dispersions have a controllable particle size in the range between 50 and 150 nm and, consequently, the deposition of layers by spin-coating or drop-casting is realized. The resultant films exhibit a particulate structure and their morphology has been characterized by means of SEM and AFM. Upon investigation of the BBL dispersions in organic field-effect transistors an ambipolar charge carrier transport has been observed, which presumably is related to the presence of mobile ions.