Rice flour was modified with water and glycerol in single-screw extruder to obtain bioplastic of low manufacturing cost. Sisal fibers were used as reinforcing fillers to enhance rice flour-based bioplastic properties. The effects of short sisal fiber content (5 to 20 wt.%), length (0.2 to 6 mm) and alkali treatment (5% w/v NaOH) on the moisture content, tensile properties, impact properties, dynamic mechanical properties and morphology of the biocomposites were studied. The results showed that incorporation of the sisal fibers with a fixed fiber length into the bioplastics improved moisture resistance, tensile strength, impact strength and storage modulus, and that the improvement level increased with increasing sisal fiber content. The optimum reinforcement was achieved at 20 wt.% of fiber loading and 4 mm long fibers. The tensile strength of the biocomposite was about 4 times more than that of the neat rice flour-based bioplastic. The use of 5% NaOH aqueous solution further improved the moisture resistance and mechanical properties of the biocomposites, mainly resulting from better interfacial adhesion between the sisal fiber and rice flour matrix. Furthermore, the performance of the rice flour-based bioplastics synergistically combined with the sisal fibers suggests that they have great potential in development of environmentally friendly/sustainable biomaterial products from renewable resources.