Abstract In this paper the investigation concerning the behavior of the clay, Palmyra fruit fiber and Bagasse based composite fired brick; also other mechanical/refractory properties of Clay were investigated. The raw clay gotten from Nalgonda in Telangana state clay brick manufacturers. It was first processed to very fine particles and characterized using SEM. Palmyra fruit fiber and bagasse was also dried to remove moisture content. The mixture of dried Palmyra fiber and Bagasse with the processed clay was mixed at various proportions with a little addition of water for plasticity. Samples of cylindrical dimensions were produced from the mounting press by the process of compaction with a very high pressure. The samples were dried and then finally fired in the furnace at 1100°C for a final curing. Properties which include thermal shock resistance, bulk density, cold crushing strength, thermal conductivity, water absorption and porosity were obtained by the appropriate standard test methods. The micro structures of the fired samples were also characterized with SEM using back scattered secondary imaging and weight loss with respect to temperature change by the TGA. The results show that the amount of Palmyra fruit fiber and Bagasse admixture affects the properties variously; porosity increases with percentage increase in Palmyra fiber and Bagasse admixture while the thermal conductivity and other properties of the sample reduce with percentage increase in Palmyra fruit fiber and Bagasse admixture.