A biodegradable polymer mud was prepared using Millet starch pre-gelatinized in the absence of a solvent. The filtration and rheological properties of the mud were studied at 25 degrees-200 degrees C temperature range and at 0.01-0.05g/mL concentration of starch using filter loss and viscometric methods respectively. Experimental results showed that the new mud has better filtration control behavior and thermal stability at all the temperatures than widely used mud prepared with hydroxy propyl-modified starch. The mud displayed thermal degradation at 200 degrees C. The values of flow index were found to be less than 1.0, showing non-Newtonian and pseudoplastic flow behavior of the mud. Shear stress and yield stress increase with increase in concentration. Viscosity decreases with increasing shear rate, showing shear thinning behavior of the mud. The polymer mud obeyed Henri Darcy and API models for static filtration as well as power law and Herschel-Bulkley models for fluid rheology. The new mud is purer and more suitable for drilling operations in environmentally sensitive areas than the widely used mud.