<b>Study the Effect of the Untreated and Treated Fly Ash on the Mechanical Properties of the Polymer Composites Based on a Mixture of Bisphenol a and Bisphenol F Epoxy Resin Cured by Kingcure K11 Hardener</b> Ordinary fly ash type C is modified the surface by the agents KOH 3M, Silane Silquest in acidic condition pH = 4 and Stearic acid 2 , respectively. Mixture of bisphenol A epoxy resin GELR 128 resin A and Bisphenol F epoxy resin EPOTEC 170LV F resin is prepared by agitating well in a glass with a agitating speed of 200 rpm at a temperature of 50°C and a time of 30 minutes. Modified fly ash was dispersed into mixture of epoxy resin and then solidified with Kingcure K11 hardener. The results showed that the mechanical properties of the polymer composites based on mixture of bisphenol A and bisphenol F with treated fly ash 10 , 20 , 30 by weight cured by Kingcure K11 hardener were higher than that of untreated fly ash composites. mixture, bisphenol A epoxy resin, bisphenol F epoxy rerin, fly ash, treated, polymer compozite 759-762 Issue-3 Volume-5 Bach Trong Phuc | Pham Duc Trinh | Nguyen Thanh Liem