Hydroxiteapatie (HA) as a filler is a mixture that is often added to alloy or composite products. This study investigates the development of polyester composites reinforced with kenaf fiber (KF) and hydroxiteapatite (HA) fillers in order to reduce their environmental impact. The strength, decomposability, and low weight of these composites make them ideal for a wide range of applications due to their exceptional mechanical properties. In addition to tensile and bending tests, water absorption tests, and immersion in seawater simulations, the composites were evaluated under demanding conditions. The water absorption rate increased with increasing fiber volume percentages in the composite, primarily due to the water-absorbing properties of the KF and HA particles. In contrast, the KF-15%HA-reinforced composite, which underwent soaking at 50 °C, exhibited the lowest tensile strength of the three composites. Additionally, the temperature at which aging occurs influences the composite's ability to absorb water and its mechanical properties. A filler may improve the mechanical properties of composites made from kenaf fibers, and it can also affect moisture absorption, reducing moisture absorption and increasing adhesion.