Sisal fiber (Agave sisalana) reinforced polymethylmethacrylate (PMMA) composites have been developed as a candidate material for biomedical applications on account of the biocompatibility and low price of sisal fiber and PMMA, and high mechanical strength of sisal compared to other natural fibers such as flax, coconut coir, and kenaf. Hydrophilicity of sisal fiber and hydrophobicity of PMMA lead to be an incompatibility between them, which is a significant problem in the composite fabrication. The addition of maleic anhydride graftedpolypropylene (MAPP) as a coupling agent is expected to be able to overcome the problem. The present work aims to fabricate and characterize the tensile and bending properties of sisal/PPMA composites with and without MAPP. The untreated sisal and alkali-treated sisal by soaking the fibers in 6% NaOH for 4 h at room temperature were used in this study. The sisal/PMMA composites with a fiber length of 6 mm and 30% fiber loading were fabricated using a cold press machine under pressure 120 kg/cm2 at room temperature for 60 minutes. In this case, various concentrations of MAPP (0, 3, 5 and 10 wt. %) were added in the raw-sisal/PMMA composites, but not in the alkalized sisal/PMMA composite. All composite specimens were mechanical tested following ASTM D638-01 and ASTM D790-02 standards for tensile and bending tests, respectively. Scanning electron microscopy (SEM) of the fracture surface was carried out on the tensile tested specimens. The results showed that alkalization on sisal fiber increased the composite mechanical strength. The mechanical strength of raw-sisal/PMMA with 5% MAPP was higher than that of 3 and 10% MAPP. The tensile strength and modulus of the composites with MAPP 5% were 44.97 MPa and 1.486 GPa, respectively. While the bending strength and modulus were 74.87 MPa and 2.121 GPa, respectively. The addition of 5% MAPP into the raw sisal/PMMA composites resulted in more effective in increasing the mechanical strength compared to the composite alkalized sisal/PMMA.