Composites of silk fibre reinforced chain extended polyurethane (CEPU) was synthesized by the reaction of castor oil with different diisocyanates and glutaric acid as chain extender. The effect of incorporation of silk fibre into neat CEPU on the physico- mechanical properties and thermal behaviours (TGA and DMA) has been investigated. The incorporation of silk fibre into CEPUs resulted in an enhancement of tensile strength and Tg. The effects of biological fluids and salt solution on swelling behavior of CEPU biocomposites were reported. Key words: Castor oil, silk fibre, composites, polyurethane, DMA, TGA.