A series of castor oil-based polyurethane (PU)/epoxy resin (EP)-graft interpenetrating polymer network (IPN) composites loaded with multi-walled carbon nanotubes (CNTs) were prepared. The damping properties, thermal stability, tensile and impact strengths, as well as fractured surfaces of the CNTs modified IPN composites were studied systematically. Results revealed that the incorporation of CNTs can improve the damping capacity especially when the CNTs content was 0.1%, though the thermal decomposition temperature decreased slightly. The storage modulus was also increased with the addition of CNTs. The mechanical properties of the modified polymer composites were improve. The tensile strength of the polymer composites increase by more than 30% compared to the matrix, when the CNTs contents were 0.1% and 0.7%. When the CNTs content was 0.3%, the impact strength of the modified composites increased by ca. 54% compared to the polymer matrix. It is expected that the modified composites may be used as structural damping materials.Highlights► We prepared a series of carbon nanotubes filled castor oil-based PU/EP graft IPN composites. ► The incorporation of carbon nanotubes could improve the damping capacity of the composites obviously. ► The incorporation of carbon nanotubes could improve the mechanical strength significantly.