The recent use of fiber optic waveguides for biochemical analyses is mainly based on light intensity changes. Waveguide ellipsometry sensors (WEFE) are proposed for biosensor applications. The WEFE is based on the principle of ellipsometry. A laser beam propagates in the waveguide with two fundamental modes: transverse electric field, parallel to and perpendicular to the sensing surface. The evanescent waves interact with the absorbed or conjugated layer of biomolecules, producing changes in the relative phase, (Delta) , and amplitude, (Psi) , upon interaction. The ellipsometric parameters change with biomolecule adsorption or conjugation on the sensing surface. From the ellipsometric parameter changes, the surface concentration, and thus the solution concentration, of the biomolecules can be estimated. Expected advantages of the WEFE are: (1) the WEFE measurement is independent of light intensity; (2) the WEFE measurement is independent of the waveguide coupler quality; (3) (Delta) is very sensitive to the thickness of the adsorbed layer, the WEFE is much more sensitive than sensors based on intensity; (4) optic fibers are commercialized, the WEFE will be easy to fabricate and use commercially. In this paper -- a comparison of WEFE within other biosensors -- the principle of WEFE including light propagation in waveguide and ellipsometry parameter analysis, the WEFE arrangement and instrumentation, and preliminary experimental results are given.