The critical coagulation concentration (CCC) of a spherical colloidal suspension is estimated. Here, the concentration of particles is high so that the classic DLVO theory, which is based on the interactions between two particles, can be inapplicable. A statistical mechanics approach based on the Ornstein-Zernike model and Percus-Yevick relation is adopted to estimate the total interaction energy. We show that, in general, the presence of the particles surrounding two interacting particles has the effect of reducing the total interaction energy between them and, therefore, of increasing the probability of coagulation. The effect of particle concentration on CCC is more significant under the following conditions: large Hamaker constant, high particle concentration, and low surface potential of the particle. The result predicted by the DLVO theory can be recovered as the limiting case of the present analysis in which the concentration of particles is low and the surface potential is high.