The effect of extraction by soil retting and chemical treatment on the mechanical properties of sisal fibre reinforced polyester composites was investigated. The sisal fibre was extracted by soil retting method followed by chemical treatments. Treatments were carried out on the fibre at an elevated temperature of 70^°C for 2 hours with 2 molar solutions each of NaOH, KOH, H₂O₂ and Ethanol. Both treated and untreated fibres were used to develop the sisal fibre reinforced polyester composites in predetermined proportions after which they were tested for mechanical properties. From the results, it was observed that, KOH treated fibre reinforced polyester composite followed by Ethanol treated fibre samples gave the best results. KOH treatment was observed to enhance the tensile and hardness properties of the polyester composites than other treatments.