Ultradrawing and ultimate tensile properties of ultrahigh molecular weight polyethylene (UHMWPE) composite fibers were successfully improved by the addition of nanoalumina (NAL), acid treated nanoalumina (ATNAL), and/or functionalized nanoalumina (FNAL). As evidenced by FTIR and TEM analyses, maleic anhydride grafted polyethylene (PEg-MAH) molecules were successfully grafted onto ATNAL fillers. The specific surface areas of FNAL fillers reached a maximal value at 516 m(2)/g, as they were modified using an optimal weight ratio of PEg-MAH to ATNAL at 8. Achievable draw ratio (D-ra) values of UHMWPE/NAL (F(100)A(y)), UHMWPE/ATNAL (F(100)A(x%-8-y)) and/or UHMWPE/FNAL (F(100)A(x%8)FPE(y)(z)) as-prepared fibers approached a maximal value as NAL, ATNAL, and/or FNAL contents reached an optimal value at 0.1, 0.1, and 0.075 phr, respectively. The maximal D-ra values of F(100)A(x%-8)FPE(0.075)(z) as-prepared fiber specimens were significantly higher than those of F(100)A(0.1) and F(100)A(x%-8)-0.1 as-prepared fiber specimens. In which, the maximal D-ra values obtained for F(100)Ax%-8FPE(0.075)(z) as-prepared fibers reached another maximal value as FNAL fillers were modified using an optimal weight ratio of PEg-MAH to ATNAL at 8. The ultimate tensile strength value of F(100)A(2%-8)FPE(0.075)(8) drawn fiber reached 6.4 GPa, which was about 2.4 times of that of the UHMWPE drawn fibers prepared at the same optimal UHMWPE concentration and drawing condition. (C) 2015 Society of Plastics Engineers