The effect of small concentrations of dicumyl peroxide (DCP) on the modification of a linear low density polyethylene (LLDPE) during a reactive extrusion process was investigated. The experiments were arranged in a two level factorial design in order to evaluate the effect of temperature zones (X-1), peroxide concentration (X-2) and screw rpm (X-3) on the modification of LLDPE. The melt flow index (MFI) was used as a response variable. It was verified that the thermal properties, crystalline melting temperature (T-m), the heat of fusion (Delta Hmelt) and the crystallinity degree (X%) decrease with the increasing of the peroxide concentration. The crystallization temperature (T-c) increased up to 0.05% w/w peroxide, whereafter the level stays almost constant. The gel content of the samples however indicated that a three-dimensional network was negligible in the experimental conditions used.