The impurity effect on the carrier transport in a 2-phenylnaphthalene derivative of 6-(4'-octylphenyl)- 2-dodecyloxynaphthlene (8-PNP-O12), which is a liquid crystalline photoconductor and we call Self-organizing Molecular Semiconductors (SOMS), was investigated with a two series of impurity materials, i.e., polyacenes and terthiophenes. The carrier transport in impurity doped 8-PNP-O12 exhibited curious impurity effects which were never observed in solid materials systems: the carrier transport was affected not only by an energy level of impurity materials but also their molecular structure; its activation energy depended not only on the energy level of impurity molecules but also on their concentration; the carriers were transported by two different mechanisms, i.e., the electronic and ionic conduction. All these unique properties are discussed in relation to the nature of liquid crystalline molecules. i.e., fluidity and self-organization.