The orientational fluctuation in isotropic toluene and dichloromethane solutions of a stiff-chain polymer, poly(n-hexyl isocyanate) (PHIC), has been studied by anisotropic light scattering up to the vicinity of the isotropic-nematic phase separation region. The depolarized component Delta R-theta,R-Hv of the Rayleigh ratio divided by the polymer concentration increased with increasing the polymer. concentration. The Delta R-theta,R-Hv data for different molecular weights were fitted almost quantitatively to the scaled particle theory for wormlike hard-spherocylinders with the hard-core diameter d, developed by incorporating the higher virial terms in the free energy. However, the fitted d value was appreciably smaller than that chosen to explain the experimental osmotic compressibilities and/or isotropic-nematic phase boundaries of the same systems. Then it was found that the "spinodal concentration" c*, where the isotropic phase becomes thermodynamically unstable, lies within the nematic region, in contrast with the prediction of the scaled particle theory that c* should be in the isotropic-nematic biphasic region. This inconsistency may come from a mean-field approximation used in the scaled particle theory.