Natural fibers are a powerful competitor in the polymer composite market due to their availability, sustainability, obtainability, cost, and biodegradability. The surface of natural fibers was changed to increase mechanical qualities, hydrophobicity, and bonding with polymer matrix. This study exposes the influence of several surface treatments of coconut tree peduncle fibers (CTPFs) on the thermomechanical and water absorption properties of CTPF-reinforced polymer composites. The CTPFs were treated with sodium hydroxide, benzoyl peroxide, potassium permanganate and stearic acid at a constant 40 wt% and individually reinforced in an unsaturated polyester resin matrix containing 60 wt% CTPFs. Chemically treated CTPFs improved reinforcement-matrix