The present study reports the development of composites of high-modulus polyethylene extrudable (HMPEX) filled with niobium oxide (Nb2O5) for using in therapeutic applications. The effect of filler content on mechanical properties of composites processed with Nb2O5 contents in the range of 5-30 wt% was evaluated. Tensile strength tests were performed according to ASTM D 638. The tensile modulus values of composites increased significantly at high filler contents (15, 20, 25 and 30 wt%), where the modulus increased 18, 16, 14 and 24%, respectively, compared with the modulus of neat HMPEX. The yield strength showed slight improvement with the increase of filler content up to 20 wt%. At this concentration, it reached the maximum value, 10% higher than the value of HMPEX. The values of elongation at break and tensile strength decreased with the increase in filler content. All properties presented by the composites processed by extrusion were inferior to those of the composites prepared by compression molding. The neat HMPEX and the HMPEX composites processed with 5 wt% of Nb2O5 obtained by compression molding exhibited properties matching those required for medical grade UHMWPE resins, according to ASTM F648-00, making them potential candidates for medical applications.