:This study concerns the melt-free radical grafting of glycidyl methacrylate (GMA) onto high-density polyethylene (HDPE). We studied the effect of two initiators (tert-butyl cumyl peroxide and di-tert-butyl peroxide) onto HDPE. Crosslinking of polymer was observed in the presence of 0.3 wt % tert-butyl cumyl peroxide but not with 0.3 wt % di-tert-butyl peroxide. The grafting was carried out in a Brabender batch mixer at 190 degreesC. The grafting yield of GMA onto HDPE (determined by infrared spectrometry) is weak (<1 wt % for an initial concentration in monomer of 6 wt %). Moreover, it was noted that the degree of grafting did not vary with the concentration and the nature of peroxide used. To increase the grafting yield of GMA, we added to the HDPE/peroxide/ GMA system an electron-donating monomer, such as styrene, Adding this comonomer multiplied the rate of grafted GMA 3- or 4-fold, resulting in a ratio [styrene](i)/[GMA](i) = 1 mol/mol with [GMA], = 6 wt %, So, the copolymerization is favored compared with the homopolymerization. This kind of copolymer presenting reactive functions is very attractive in the field of compatibilizing immiscible polymers.