Studies have been carried out on polyurethane elastomers based on modified castor oil in combination with different molecular weights of polyethylene glycol and polymeric methylene diphenyl-4,4′-diisocyanate (PMDI). The resulting polymers were cast into molds and the moldings were characterized by scanning electron microscopy and thermogravimetric analysis. Mechanical properties such as tensile strength, elongation at break, hardness, abrasion resistance, and compression set were measured. There is an increase in the flexibility of polyurethanes with increase in molecular weight of PEGs added to modified castor oil.