Negative field dependence of hole mobility was observed in poly(methylphenylsilane) (PMPS) films doped with a plasticizer, dioctyladipate (DOA). By analyzing the hole mobilities in the framework of Bässler's disorder formalism, the negative field dependence was found to be due to the large increase in the parameter Σ, the positional disorder of hopping site distance. Furthermore, we succeeded in measuring the hole mobility of DOA-doped PMPS film under elongation. In UV absorption and fluorescence spectrum measurements of the elongated film, a red shift of the absorption edge was observed only for the polarized light parallel to the elongation axis, and a new emission appeared at the longer wavelength, suggesting that the molecular orientation and the extension of σ-conjugation length occurred with film elongation. The effect of film elongation was well reflected in the parameters in the charge transport expression for amorphous materials based on Bässler's disorder formalism.