Considering the remarkable growth of steel produstion, lower grade iron ore resources have been required to be extensively utilized. In addition, lowering of coke consumption in the sintering process is another demand from the viewpoints of energy FeO bearing materials, e. g., millscale and partially reduced iron are focused as a altenative agglomeration agents of coke. Fundamental study on changes in structure and pressure drop of the sintering bed was carried out using lab-scale differential type sintering simulator. In the experiment, Coke, Metallic iron, FeO and CaO particles and model mini-pellet (Alumina Cored pellet: ACP) made of alumina ball as a nuclei particle and fine mixture of CaO and Fe2O3 as adhering shell are used as raw materials. When using (ACP + Coke), pressure drop increased until ACP started to melt. Then, it decreased gradually. (ACP + Metallic iron) showed similar behavior to (ACP + Coke) at the first step but it increase again and showed a second peak. (ACP + FeO) did not show significant change in pressure drop and structure of the bed through melting process. In contrast, such changes were clearly observed in the case of CaO addition. These results shows that existing state of CaO component strongly affects the structural change of sintering bed.