Birefringence induced by the sinusoidal electric field (the Kerr effect) was studied in the dilute solutions of the fractions of disubstituted polyacetylene, poly[1-(trimethylsilyl)-1-propyne]. It was shown that the electric field-induced orientation of macromolecules exhibits a large-scale character. In the Gaussian region of chain lengths, the specific Kerr constant was found to be dependent on the molecular mass of the polymer. This trend is not predicted by current theories developed for the electrooptical properties of polymers. The features of the dipole structure and the stereoregularity of the polymer chain are considered to be the possible reasons for this phenomenon.