The rapid technological development made the industries compete to create newer innovations, to improve product quality, competitiveness, and environmentally friendly. One of the innovative materials is the material for biomedical device application, which was previously made of metal materials. However, metal materials are easily corroded, heavy, and expensive. Thus, it now began to switch to the natural fiber composite materials, due to their strength, light weight, flexibility, corrosion resistance, and wear resistance. Objectives of this research are to fabricate the high-density polyethylene (HDPE) hybrid composites reinforced with sisal and carbon fibers and to study the influence of carbon fiber length on the bending properties and water absorption of the composites. The sisal/carbon/HDPE hybrid composites were fabricated by hand lay-up method in a hot press molding at 140 oC and 1,5 MPa for 15 minutes with the fiber content of 20% and sisal to carbon ratio 3:1. Sisal fibers were alkali treated by soaking the fibers in 6% NaOH for 36 hours, whereas carbon fibers were treated in liquid nitrogen for about 10 min, and then chopped in various fiber length 6 mm, 10 mm, and 15 mm. Bending and water absorption tests were conducted on all hybrid composite specimens according to ASTM D790 and ASTM D570, respectively. The characterization of the fractured structure of the bending test specimens was carried out from the cross-section view with an optical microscope. The results showed that the highest bending strength (38.9 MPa) and modulus (3,024 GPa) of sisal/carbon/HDPE hybrid composites reached by the composite with 15 mm carbon fiber length. This composite also showed the lowest water absorption and thickness swelling of 9.37% and 4%, respectively. Those results are related to the even fiber distribution in the matrices