Chain-extended polyurethane (PU) elastomers were prepared using castor oil with 4,4'-methylene bis (phenyl isocyanate) (MDI) as a crosslinker and 4,4'-diamino diphenyl sulphone (DDS) as an aromatic diamine chain extender. A series of starch-filled (from 5 to 25% wt/wt) diamines chain-extended PUs have been prepared. The starch-filled PU composites were characterized for physico-mechanical properties viz, density, surface hardness, tensile strength, and percentage elongation at break. Thermal stability of PU/starch have been carried out by using thermogravimetric analyzer (TGA). Thermal degradation process of PU/starch were found to proceed in three steps. TGA thermograms of PU/starch shows that all systems were stable upto 235degreesC, and maximum weight loss occur at temperature 558degreesC. The microcrystalline parameters such as crystal size () and lattice strain (g in %) of PU/starch have been established using wide-angle X-ray scattering (WAXS) method. (C) 2003 Wiley Periodicals, Inc.