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Tough and strong natural fiber enhances the mechanical strengths of gluten. Reinforcement?hydrophilic matrix interaction impedes water absorption. Reinforcement?plasticizer interaction suppresses the efficiency of plasticizer. Efficiency of silane increases when the roughness of natural fiber increases. Alkali treatment for natural fiber lowers the coupling agent dosage required.This work aims to enhance the mechanical properties and water resistance of wheat gluten (WG)?based bioplastic with the addition of oil palm fiber (OPF) and surface treatments. Due to the porous surface of OPF, alkali treatment enhanced its surface area and roughness. Alkali pretreatment effect on silane efficiency was investigated using different surface treatment methods: alkali treatment, silane treatment, and silane treatment with alkali pretreatment. Neat WG and WG/OPF composites were prepared by compounding with an internal mixer and forming them with a compression molding machine. Tensile and impact testing, scanning electron microscopy, water absorption, differential scanning calorimetry, and thermogravimetric analysis were used to assess the effects of OPF content and surface treatment methods. The results suggested that the tensile modulus and strength, impact strength, and glass transition temperature of WG composites tended to increase with increasing OPF content, whereas the decomposition temperature slightly changed. OPF improved the brittle and water resistance being disadvantages of WG. The most efficient surface treatment methods are 5?wt% silane treatment and 3?wt% silane with alkali pretreatment. This indicated that the increases in surface roughness and area of OPF after alkali pretreatment enhanced the silane efficiency and reduced the dosage of silane used.