Control of physicochemical structure of fine particles based on the self-organization attracts a great interest. In particular, complicated geometry and ordered distribution of chemical elements formed by reaction-diffusion kinetics will be quite useful to develop a novel process for the particle technology. In this work, diffusion-limited growth of solid solution (Ba, Sr)SO4 was investigated. The cations diffused into gelatin from the end of a gel column, and the anion SO42-also diffused into the gel from the opposite end. Various kinds of particles with fine and complicated structures and with peculiar chemical distribution were obtained. The characteristics depended not only on the physicochemical properties of gelatin but also on the location of the particle growth. Particle structures changed by the reaction time with the complicated process. All of the characteristics were able to be understood by an assumption: the dependencies of the diffusion rates of the cations on the physicochemical properties of gelatin may be different from each other, which results in the complicated behavior of the particle growth. We were able to show a possibility to accomplish a single new process based on the reaction-diffusion process in order to obtain fine particles with novel characteristics.