A multiple-beam interference Fizeau fringes technique is used to measure the refractive index profile of drawn polyethylene fiber. The interference fringe shift in the fiber region has been analyzed automatically using an interactive algorithm. The method takes into consideration the refraction of the light beam when crossing the fiber. Plane polarized light vibrating parallel and perpendicular to the fiber axis are used to obtain the refractive index profiles of both cases. These profiles are used to determine some optical parameters such as the birefringence, the optical orientation function, the polarizability per unit volume, and the value Delta alpha/3 alpha(o), which related to the material structure. The reliability of the method is tested considering the results of drawn polyethylene fiber samples using the manual technique.