A honeycomb structure body has promoter particles made of ceria-zirconia solid solution, and inorganic binder particles made of alumina arranged between the promoter particles, and a cerium aluminate phase formed on a boundary surface between the promoter particles and the inorganic binder particles. Further, a method of producing the honeycomb structure body has at least first and second steps. The first step molds raw material to form a honeycomb molded body. The raw material has a mixture of promoter particles and a sol containing inorganic binder particles. The second step fires the honeycomb molded body in an atmosphere having an oxygen concentration of not more than 0.5 vol. % to produce the honeycomb structure body.