We conducted dynamic viscoelastic and birefringence measurements for dynamically homogeneous mixtures, polystyrene (PS)/4-pentyl-4'-cyanobiphenyl (5CB), to examine the orientational coupling between PS segments and 5CB molecules. It was also investigated whether dynamic homogeneity was correlated with orientational coupling We determined stress-optical coefficients C-R of the PS/5CB mixtures in the rubbery region With increasing the 5CB concentration, CR increased indicating the cooperative orientation of the 5CB molecule along with the PS segment to some extent We proposed a new method to quantitatively evaluate the orientational coupling, referred to as a nematic interaction (NI), between polymer segments and low-mass molecules in the mixtures From the concentration dependence of CR Using the proposed method we determined the NI parameter between PS and 5CB, epsilon(PS,SCB) The determined epsilon(PS,SCB) value was smaller than (about 1/4 of) that between PS segments (epsilon(PS,Ps)) suggesting the weaker NI acting between different chemical species with different shapes and sizes Furthermore, this result means that dynamic homogeneity is not con elated with the value of a NI parameter