The instability at the boundary of particulate zone in gel, which is formed by the reaction-diffusion kinetics, is found. This takes place within a restricted region of the electrolyte concentrations in the reservoir. This suggests the presence of an excess energy in the boundary of the particulate zone. Possible explanations are discussed on the origin of the excess energy. This may be related to pattern formations of particulate zone in gel, which has provided a fundamental interest in science and technology for long years.