In this study, use of waste produced in biodiesel production plants, as spent earth from biodiesel filtration and the by-product of glycerine, in producing lightweight structural bricks have been investigated. XRD. XRF and TGA-DTA analysis of the waste and clay were performed. Samples containing up to 20 mass% spent earth from biodiesel filtration and up to 15 mass% glycerine have been fired at 1050 degrees C to produce pores and contribute to auto-thermal combustion due to its high heating power, which involves lower fuel consumption during firing step. Loss on ignition, linear shrinkage, bulk density, apparent porosity, water absorption, water suction, compressive strength, microstructural properties and thermal conductivity values of the fired samples were investigated. The results obtained showed that the use of waste decreased bulk density and increased apparent porosity of sintered samples. Values on mechanical properties decreased, due to the increase in water absorption and water suction, but were higher than those required by the standards. Thermal conductivity of the mixture brick decreased by 20% when spent earth from biodiesel filtration was incorporated, and up to a 40% when glycerine was added. Therefore, biodiesel waste is suitable as secondary raw materials in ceramic brick production. (C) 2011 Elsevier B.V. All rights reserved.