Com. potato and corn starches were added (up to 10% by mass) to ester urethane prepolymer during its synthesis from (p-NCOC(6)H(4))(2)CH(2) and alpha,omega-dihydroxyoligo(ethylene butylenes adipate) at 80 degrees C for 1 h and (CH(2))(4)(OH)(2) in presence of 1,4-diazabicyclo[2.2.2] octane. The composite materials were studied for hardness, elasticity, tensile and tearing strength. The starch addn. resulted in decreasing the mech. strength and increasing the H(2)O absorption in the polyester urethane elastomers.