We have investigated features of liquid crystalline materials for organic polycrystalline field effect transistors (OFETs) with a model liquid crystalline material of 5,5''-dioctylterthiophene (8-TTP-8). Bulk mobility in polycrystalline thin films of 8-TTP-8 via its liquid crystalline phase was easily determined by time-of-flight experiments. Furthermore, we could evaluate impurity contamination that caused electrically active trap states in the films by analysis of transient photocurrents in liquid crystal phase. We could fabricate uniform and less defective polycrystalline thin films for OFETs by spin-coating its solution at liquid crystal temperatures, with which we fabricated OFET exhibited high mobility of 0.18cm2/Vs.