Fiber-reinforced polymer matrix composite materials gained importance because of their light weight. Also, the current research is focusing on making eco-friendly composites. Natural fibers extracted from cultivated plants are abundant, they are biodegradable and recyclable. The aim of this work is to fabricate coir fiber-based hybrid polymer matrix composites and to study their flexural behavior. A hybrid polymer matrix is prepared by blending natural resin (cashew nut shell liquid) with synthetic resin (polyester resin). The coir fiber is treated with NaOH alkali solution to improve its adhesiveness and strength before its reinforcement with matrix. The concentration of NaOH in the alkali solution and duration of treatment of the fiber in the alkali solution have been varied and its effect on the flexural behavior has been studied. A three-point bending test has been carried out on the composite using an INSTRON machine to study its flexural behavior. Using the ANOVA technique, the influence of different parameters on the flexural stress is investigated, and a regression equation has also been obtained indicating the influence of parameters. © 2015 by Begell House, Inc.