A series of polyaniline (Parri)-filled chain extended polyurethanes (PUs) were prepared by condensation polymerization of castor oil with methylene diisocyanate (MDI) as crosslinker and diamino diphenyl sulfone (DDS) as chain extender. The effect of different amounts of Pani (varying from 5% to 25%) on the chain extended PUs has been reported. The Pani-filled chain extended PU sheets were characterized by their physico-mechanical properties such as density, tensile strength, percentage elongation at break and surface hardness. Electrical properties, such as volume and surface conductivity, also have been reported. These results are corroborated with microcrystalline parameters of PU/Pani estimated using wide angle X-ray scattering (WAXS). (C) 2004 Society of Plastics Engineers.