 The study aimed to improve the durability of natural fiber UPR composite applications by investigating the mechanical, flexural, hardness, and impact properties and interfacial adhesion of acetic anhydride, AC, and ethylene-diamine tetraacetic acid, EDTA, treated cis as popl near fiber and saturate polyester UPR composites. UPR composites were prepared using hand layup technique with untreated and optimally treated fibers, and optimization of mechanical properties and interfacial adhesion was determined through response surface methodology and fiber pull-out method, respectively. The results showed that AC and EDTA treated fibers improved the flexural and hardness properties and interfacial adhesion at reduced impact strength, which was corroborated with the morphology of the composites. This article was authored by Taufik Ollidimajiez, Dominic Obchukwa Onukwili, Joseph Tagbone-Norban, and others.