A sintering aid for promoting sintering of ceramic particles and fine particles that are the same materials as ceramic particles and have smaller average particle diameter are mixed to obtain a puddle. The average particle diameter of ceramic particles is preferably about in a range of 5 to 100 μm; the average particle diameter of the fine particles is preferably about in a range of 0.1 to 1.0 μm, and the average particle diameter of the sintering aid is preferably about in a range of 0.1 to 10 μm. As the sintering aid, for example, alumina is used. This puddle is extrusion molded into a honeycomb shape and the molded object is fired at a firing temperature lower than a temperature for sintering without mixing a sintering aid. The thermal conductivity of the obtained honeycomb structure 10 shows about 60% or more of the thermal conductivity of a fired body fired without adding a sintering aid to ceramic particles and shows about 12 W/m·K or more at 20° C.