Within the range of the flow synthesized doped hydrotalcites we observed high sample crystallinity, high surface area and pore volumes. We obtained trends of thermal stability and proposed a simple geometrical explanation for the formation of the pore structure of the hydrotalcites materials. Crystallite size, shape and pore structure are all important technical characteristics of the final materials for most applications, such as electronics, ion-exchange and catalysis. The flow synthesis method allows to obtain materials with a high degree of crystallinity for various compositions. The crystallite sizes vary within 2.5 nm for all the different compositions. However, the pore sizes and, hence, the agglomerates of the crystallites vary significantly. For the conditions of flow synthesis used in this study, we conclude that the formation of the secondary structure is strongly dependent on the composition and conditions of post-synthesis (aging) when conditions of the flow co-precipitation are fixed at the characteristic time of micromixing.