Highly crosslinked epoxy resin for engineering applications is normally stiff but brittle. Therefore, many attempts have been made to improve its toughness. Nowadays, several studies have been done on toughening epoxy resin using natural rubber (NR) because it is abundant and comes from renewable resource. In the present work, NR was subjected to depolymerize in order to achieve molecular dispersion of NR in epoxy matrix. Depolymerized natural rubber (DNR) was prepared by adding a carbonyl compound to natural rubber latex solution and subjecting the mixture to air oxidation in the presence of a radical forming agent at 70°C. In addition, the interfacial adhesion between rubber and matrix must be present to achieve a significant increase in toughness. Hence, DNR was further functionalized by grafting with monomer mixture of methyl methacrylate (MMA)/glycidyl methacrylate (GMA) (90/10 wt/wt%) in an amount of 50% based on rubber content. Solution polymerization was used to graft such monomers using 2 hours reaction times at a reaction temperature of 80oC. Two types of initiator used were benzoyl peroxide (BPO) and azo-bisisobutyronitrile (AIBN). The amounts of initiator in the grafting process were 1, 2, and 3 parts per hundred of DNR. Effects of type and concentration of initiator on grafting efficiency of MMA/GMA monomer mixture onto depolymerized natural rubber were studied by proton nuclear magnetic resonance (1H-NMR) analysis. The molecular weight of DNR was characterized by gel permeation chromatography (GPC). The results indicated good evidence for the formation of graft co-polymers in the presence of both initiators, AIBN or BPO. However, the amounts of grafted MMA/GMA on DNR backbone using BPO was higher than those on DNR backbone using AIBN.