Epoxies are defined as well-established thermoset cross-linked polymers in which the cross-linking is derived from reactions of the epoxy group. Commercial epoxy resin contains aliphatic, cycloaliphatic, or aromatic back bones. The most widely used is epichlorohydrin and bisphenol-A derived resin. Epoxies were developed, principally by Ciba AG (Switzerland) and the Dovoe and Raynolds Co. (USA) [1-3]. Epoxy resins consist of threedimensional networks or agglomerates of moderate molecular weight. As the molecular polymerize through crosslinking, their rotational and rotational freedom is reduced, which reduces the chances of the primary bonds to be set up with adjacent molecules. The tensile and comprehensive strength of epoxy resins are increased if the distance between crosslinks is shortened. Shorter crosslink distances imply high volume concentration of epoxy group and hence a higher probability of reaction of all the epoxy groups. Epoxy resin also have good properties with good stiffness, specific strength, dimensional stability, high heat distortion temperature and chemical resistance [1, 4-5, 21]. For these reasons, it is also the most common polymer used in fibre and filler reinforced polymers for structural applications. However, epoxy is known to be brittle with poor mechanical properties, in terms of strength and toughness, thus preventing the use of this polymer in applications that require stability and high mechanical performance. Many researchers reported that to toughen epoxy resin, a common method is introducing particles in the resin, including liquid rubbers, thermoplastics, copolymers, silica nanoparticles, silicate layers, core shell particles, and combinations of these [6-10]. Synthetics rubbers containing methyl, hydroxyl, carboxyl, anhydride or thiol groups potentially react with the epoxy resins. Barcia et al. [11] used hydroxyl terminated polybutadiene (HTPB) as surface modifier in carbon fiber reinforced, epoxy matrix composites. Rubbers with carboxyl groups in the chain however may be cured with the epoxy resin to increase elongation and to decrease the tensile strength and hardness. Bussi and Ishida [12] studied the mechanical properties of the blends of diglycidyl ether of bisphenol-A (DGEBA) based epoxy resin and hydroxyl terminated, internally epoxidized polybutadiene rubber. In order to improve mechanical properties, the epoxidized rubber was pre-reacted with an excess diepoxide to achieve better bonding between the rubber particles and the epoxy continuous phase. Nigam et al. [13] studied the changes in mechanical properties of epoxy cresol novolac (ECN) resin by liquid carboxy terminated copolymer of butadiene acrylonitrile (CTBN) modification. Extensive study had been carried out to increase the toughness, and these include using glass beads, alumina Abstract: Epoxy matrix widely used in polymer composites as a reinforcement material due to its outstanding performance. Epoxy matrix exhibit good mechanical and thermal properties such as good stiffness, dimensional stability and high heat distortion temperature. However, it is known that epoxy had brittleness and exhibit low toughness. This study investigates the mechanical properties of brittle epoxy resin when modified by liquid epoxidized natural rubber for toughening purposes. Liquid epoxidized natural rubber (LENR) was introduced to the epoxy with five different loadings of 1%, 3%, 5%, 7% and 9% by weight. The mechanical strength (flexural strength, flexural modulus, tensile strength, tensile modulus and impact strength) of the rubber toughened epoxy composites were investigated. The results showed that the addition of liquid epoxidized natural rubber (LENR) had improved the flexural modulus, flexural strength and impact strength by 47%, 40%, and 22% respectively at 3% loading.