In the present study, high density polyethylene (HDPE)-based composites containing different amounts of fumed silica (FS) were prepared by melt compounding in a corotating twin screw extruder. Polyethylene-g-maleic anhydride copolymer (PE-g-MA) containing 1 wt% maleic anhydride was used for interface modification between filler and polymer. The interaction between the surface hydroxyl groups of fumed silica nanoparticles with maleic anhydride groups of PE-g-MA led to a finer dispersion of the filler in the HDPE matrix. The terminal complex viscosity and terminal storage modulus were highest at 1 wt% filler loading due to widely spread network formation by FS nanoparticles. This filler network plausibly got disturbed at higher filler content and/or interface modification which was reflected in their stress relaxation behavior also. The dynamic rheological behavior of the composites was explained in terms of morphological observations. POLYM. ENG. SCI., 2013. (c) 2012 Society of Plastics Engineers