Abstract: Cordierite was synthesized from three main starting materials: the waste slag of an aluminum factory, talc powder and clay. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the crystal structure and microstructures. The amount of each crystal phase was calculated by Rietveld Quantification. The parameters of the unit cell for each crystal phase were determined using Philips X'pert plus software. The results show that the synthesized cordierite possesses the same hexagonal structure as pure cordierite (space group P6/mcc) with only a slight variation of lattice parameters. The results also reveal the existence of some mullite solid solution and Mg-Al spinel in the sample. The maximum amount of cordierite(86;) was obtained through the recipe corresponding to sample No. 3, in which the optimum amount for talc powder, clay, waste slag and quartz are 22.0;,24.0;,48.0; and 6.0; respectively. The crystal structures for all the byproducts are conventional except for slightly distorted lattice parameters and volume.