The work entailed the influence of particle size on the characteristics and water absorption resistance of avocado pear wood fiber/low-density polyethylene (APWF/LDPE) composite enhanced by pretreatment. The fiber particle of 100, 80, 60, 40, and 20 mesh (150, 180, 250, 425, and 850 µm) for the avocado wood fiber (APWF) was infused in the resin. Each particle of the fiber with fiber content of 5–25 wt% for the untreated, pretreated with NaOH, NaOH + CH3COOH, and NaOH + CH3COOH + MAPE was intermixed in the resin to produce the APWF/LDPE composites, respectively. The APWF/LDPE composites were analyzed on the properties, water absorption resistance, Fourier transform infra-red, and scanning electron microscopy. The study exhibited that mechanical properties and water absorption resistance of the APWF/LDPE composite were improved at lower particle of the fiber triggered by treatment. The best properties were confirmed at 150 µm of APWF pretreated with NaOH + CH3COOH + MAPE when compounded with the resin. These were proportional to 15.92 MPa, 0.867 GPa, 41.39 MPa, 0.662 GPa, 683 Pa, 84.04 kJ m−2, and 2.44 % for tensile strength, elastic modulus, flexural strength, bending modulus, Brinell hardness, impact strength, and water absorption resistance, respectively. The APWF/LDPE composite for NaOH + CH3COOH + MAPE pretreated is recommended for interior cabinet of an automobile.