Biopolyesters based on the fumarate ester of castor oil and methylolated cardanol such as poly(castor oil fumarate) biopolyester resin and poly(cardanol fumarate) biopolyester resin were prepared using naturally available byproducts like castor oil and cashew nut shell liquid (cardanol).The Physico Chemical Properties of these biopolyester resins were studied under standard conditions.