Flow birefringence of dextran solutions in dimethylsulphoxide was studied and the intrinsic optical anisotropy (α₁-α₂) of its chains was determined to be +12.5×10^-25 cm³. The dependence of birefringence in dextran films of different thickness on the angle of incidence of polarized light was then studied and the surface birefringence of the film was determined. The dependence of surface birefringence on film thickness has made it possible to determine the effective thickness of the anisotropic near-surface layer, while the comparison of the surface birefringence with the value of (α₁-α₂) enabled the estimation of the orientation of the molecular fragments with respect to the film surface.