Dielectric dispersions were measured for a semiflexible polymer, poly (n‐hexyl isocyanate) (PHIC), in dilute through concentrated, isotropic solutions. Since PHIC has a dipole moment parallel to the chain contour, its dielectric dispersion reflects the fluctuation of the end‐to‐end vector of the polymer. For lower molecular weight PHIC samples with rodlike nature (the Kuhn statistical segment numberN≤0.53), the dispersion for the permittivity ε’and the loss factor ε‘almost obeyed the simple Debye relation irrespective of the polymer concentrationc, and thecdependence of the dielectric relaxation time τDwas favorably compared with the fuzzy cylinder model theory. On the other hand, for higher molecular weight PHIC samples (N≥0.69), the dispersion curves for ε’and ε‘deviated from the Debye relation and thecdependence of τDdid not agree with the prediction of the fuzzy cylinder model theory. These disagreements may ascribe to the chain flexibility effect for the higher molecular weight samples.