The effect of starch volume fraction on starch-filled poly(hydroxy ester ether) (PHEE) biodegradable composites was analyzed using Mooney, Thomas, Maron & Pierce, and Frankel & Acrivos equations. Corn starch/PHEE materials were extruded using a twin-screw extruder with starch volume fractions from 0.27 to 0.66. The starch was dried to a moisture content of 0.7% to minimize moisture effect on composite rheology. Dynamic frequency sweep measurements were carried out at 120 degreesC and 1% strain. The equations of Maron & Pierce, Thomas, and Frankel & Acrivos can be used to describe the experimental data. It is found that the relative viscosity at the same shear stress increases with increasing shear stress. The possible existence of yield stress at high starch concentrations was examined using a Casson plot.