Recently, with the growing demand for reduction of kiln heat loss, lightweight monolithic working lining with low thermal conductivity and low bulk density were proposed and developed. These refractories were expected to decrease the kiln heat loss and specific refractory consumption per ton of products. To improve the energy-saving capacity of aluminosilicate refractory castables for working lining of high-temperature kilns, this study presents the researches on structure, microstructure and properties of lightweight aluminosilicate refractory aggregates and castables. Firstly, the lightweight aggregates were produced using the high-quality kaolin and the porogenous material using high temperature processing and investigated in terms of XRD-mineralogy, pore structure and chemical composition. Secondly, the lightweight castables with different particle size distribution, as per Dinger and Funk model, were designed to attain different flow consistency. Both calcium aluminate cement (CAC)-containing and cement-free monolithics were processed conventionally and heat treated at temperatures between 110-1200°C. The samples of precast refractory shapes were investigated in terms of physicomechanical and thermal properties, XRD-mineralogy, microstructure-SEM/EDS and corrosion resistance. Moreover, a comparative study on lightweight and dense aluminosilicate castables was done. In conclusions, the lightweight specimens exhibited high strength, excellent thermal shock resistance, low thermal conductivity and good corrosion resistance, which can meet the requirements for furnaces for thermal treatment of steel.