Linear medium density polyethylene (LMDPE) was functionalized with allyl glycidyl ether (AGE) in an internal laboratory mixer in the presence of peroxide. AGE is a bifunctional monomer, which forms unstable and energetically rich macroradicals. Upon increasing the peroxide content chain scission and grafting yield were favored. The degree of functionalization was determined by means of a calibration function for Fourier-transformed infrared spectroscopy (FTIR). Grafting AGE onto LMDPE led to a small loss of crystallinity, as evidenced by differential scanning calorimetry (DSC) and X-ray diffractometry analyses. Composites of LMDPE or functionalized LMDPE-AGE and cellulose were prepared in the mixer with filler contents ranging from 20 to 50 wt%. Composites of AGE functionalized LMDPE and filler content higher than 30 wt% presented tensile properties superior to that observed for composites with unmodified LMDPE. Scanning electron microscopy (SEM) on the composites fracture surface evidenced good interfacial adhesion between LMDPE-AGE and cellulose fibers. (c) 2005 Elsevier Ltd. All rights reserved.