We first investigated the dipolar-dopant effects on the electronic charge transport in mesophases. We used phenylnaphthalene derivatives as a host smectic liquid crystal and cyanobiphenyls as a variable dipolar guest, and characterized the charge carrier transport properties of doped smectic mesophases by time-of-flight experiments. Comparing the experimental results with analytical calculation based on Gaussian disorder model, we found that the effect of dipoles is well explained by additional energetic disorder induced by carrier-dipole interaction, and that the induced energetic disorder is proportional to the square root of the dopant concentration c (c1/2) for smectic mesophases, while it is proportional to c2/3 for non-oriented materials. This indicates that the ordered molecular alignment in smectic mesophases lowers energetic disorder. This study gives us an insight into the effect of dipoles in ordered molecular systems and the better molecular design of liquid crystals as an organic semiconductor.