Dodecyl benzene sulfonic acid (DBSA) doped polyaniline (PANI) grafted MWNTs (PANI-g-MWNTs)/Epoxy composite were prepared by aniline in situ polymerization in the presence of phenylamine groups contained MWNTs followed by solution blending and mould casting. Phenylamine groups grafted on the surface of MWNTs via amide bond join in the in situ polymerization and MWNTs are encapsulated by PANI coatings forming a core (MWNTs)-shell (PANI) nano-structure. DBSA doped PANI coatings swell in tetrahydrofuran (THF) and core-shell nano-structures are stabilized in epoxy solution, which is in favor of MWNTs dispersion in epoxy resin and formation of a homogenous MWNTs/Epoxy composite. After DBSA doped PANI-g-MWNTs are introduced in Epoxy, initial curing and exothermic peak temperatures as well as curing reaction enthalpy decrease, which indicates addition of DBSA doped PANI-g-MWNTs promotes curing reaction of Epoxy. Tensile strength, Young’s modulus, elongation at break, flexural strength and flexural modulus of the composite are improved by 71.7%, 42.3%, 99.8%, 55.01% and 39.86% compared with Epoxy, respectively.