Using a stretched-polymer-film technique, we could assign the resonance fields in the electron paramagnetic resonance (EPR) spectra of the lowest excited triplet (T-1) states of p- and m-polyphenyl molecules [C6H5(1,4-C6H4)(n-2)-C6H5, C6H5-(1,3-C6H4)(n-2)-C6H5, respectively] relative to the spin axes. In this case, the set of the zero-field splitting (ZFS) parameters is unique for a p-polyphenyl molecule but not for a m-polyphenyl molecule composed of more than three benzene rings. Taking the z axis as being perpendicular to the molecular plane and the x axis as being rather close to the longest direction of the molecule, we obtained interesting relations of the ZFS parameters to the conformation. The present calculations showed that for p-polyphenyl molecules the conjugated system is delocalized along the longest molecular axis and the \Z\ values decrease by an increase of the composing benzene rings and that for the m-polyphenyl molecules the T-1 character is localized at every composing biphenyl skeleton and the \Z\ values are almost unchanged. Concerning the relative values of ZFS parameters, we obtained that \X\ > \Y\ for p-polyphenyl molecules whereas \X\ < \Y\ for m-polyphenyl molecules. Adopting both the valence-bond and the molecular-orbital approximations, we clarified that such a difference arises from the deformation of the molecular structure by the steric hindrance among the composing benzene rings. In this case, we emphasized that the influence of the bond angles of the composing benzene rings is especially important in discussing the ZFS parameters of polyphenyl molecules in their T-1 states. Such a relation is illustrated by using the ZFS parameters. of the deformed biphenyl molecule. Comparing the different sets of the ZFS parameters of a m-polyphenyl molecule, we clarified the existence of its conformers, which were assigned to their respective conformations, although the observed set of the ZFS parameters cannot always correspond to the single conformation.