In this outline, the stability of solid/liquid dispersion was theoretically investigated the matter from all angles by using the modified DLVO theory. The stability was handled various considerations such as a production and characteristics of electrical double layer, total interaction$(V_T)$ that consisting of attractive force$(V_A)$ and repulsion$(V_R)$. coagulation, the stability ratio(W), critical flocculation concentration (cfc) and zeta potential$(zeta)$ etc. It was possible for us to examine with the stability ratio(W), critical flocculation concentration (cfc) and zeta potential$(zeta)$ that may estimation of stability of solid/liquid dispersion experimentally.