Polarizabilities and dipole moments of hole transport molecules with different mobilities were measured. The zero-field mobilities of the molecularly-doped polymers increase with increasing polarizabilities and decrease with increasing dipole moments of the dopants. Concerning molecules with similar dipole moments, mobilities correlate well with polarizabilities. Also concerning molecules whose polarizabilities are almost equal, the correlation between mobilities and dipole moments is clear. The 3-D plot of the mobility as a function of the polarizability and the dipole moment is nearly coplanar. Within a framework of the small polaron formalism, polarizabilities are good indices to evaluate the degree of electron cloud extension that affects transfer integral J. On the other hand, the magnitude of the polaron binding energy E_p is macroscopically influenced mostly by the intramolecular structural relaxation. However, we propose that the E_p has a distribution caused by intermolecular interactions, which is not considered in the small polaron formalism. Such distributions, which have recently been discussed within a framework of the disorder formalism, are due to the random internal field caused by the local charge-dipole interaction. These analyses support the experimental data that the logarithm of mobility is described as a linear combination of the polarizability and the dipole moment.