On the basis of the nonlinear reaction-diffusion kinetics, spontaneous formation of physical/chemical microstructure can be introduced into fine particles formed in a homogeneous hydrogel. In this paper, we discussed the structure and chemical distribution within the particles formed by the diffusion of Ba2+ and Sr2+ ions and SO42- ions in opposite directions in agar gel and agar/gelatin mixed gel. In agar gel, the structure of a particle depends strongly on its position in the gel, i.e., structures with extensive diversity are obtained. This is the same trend as that found in the single-component gel of gelatin. In mixed gel, however, the particles are formed only in a narrow range of the gel, and hence the structure of the particle does not exhibit such diversity. This result may give fundamental information applicable to the design of a reaction-diffusion system for the particle formation; how particles with different structures are formed at different positions in a gel or how such diversity of particle structures can be avoided.