Abstract: Using maleated castor oil (MACO) as main raw material, enviromental friendly CaCO₃/MACO composites and their foam plastics were prepared with inorganic filler calcium carbonate (CaCO₃) particle as reinforcement. Effects of addition of CaCO₃ on mechanical properties, dynamic mechanical performance and thermal stability of MACO were analyzed. And the interfacial interaction between inorganic particles and matrix was analyzed. The results show that CaCO₃ content and the interfacial bonding between CaCO₃ and MACO matrix are the key factors influencing the strength of composites. With increasing of CaCO₃ content, stiffness of CaCO₃/MACO composites increases significantly. At 60% mass ratio of CaCO₃ loading, tensile and bending strength attain the maximum values of 26.7 MPa and 46.2 MPa, respectively, which are comparable to some general commercial plastics. Dynamic mechanical analysis and thermal stability analysis show that the addition of CaCO₃ improves storage modulus, glass transition temperature and thermal decomposition temperature of maleated castor oil matrix plastics. These behaviors are attributed to the good interfacial adhesion between CaCO₃ and the carboxyl, carbonyl of MACO resin by hydrogen bonding and coordination bonding. CaCO₃ can also reinforce CaCO₃/MACO composite foam plastics. When density of foam plastics is 0.24 g/cm³, by adding 20wt% of CaCO₃, compared with pure foam plastics, the compressive strength and modulus of the composite foam plastics are increased by 142.0% and 211.5%, respectively. The addition of inorganic filler into castor oil derived polymer can reduce the usage of petroleum based components and the cost of material, while increase compatibility of CaCO₃/MACO composites with environment.