In tumor cells, apoptosis is hindered because of the inability of their mitochondria to release cytochrome c (cytC). The induction of apoptosis can be achieved by introducing external cytC into the cells through the uptake of cytC-bearing particles by phagocytosis. Therefore, we use the mineral montmorillonite (MM), which has high adsorption capacity due to the huge size/thickness ratio of its plate-like colloid particles. After cytC adsorption onto half-micrometer size MM monoplates, the hybrid cytC-MM particles acquire antitumor properties due to the capability of cancer cells to phagocytize particles with submicron size. Normal cells, except for those of the immune system, lack the ability to phagocytize colloid particles, providing them with protection against the cytotoxic effect of the cytC-MM nanoplates and high selectivity at anticancer treatment. We applied physicochemical techniques including microelectrophoresis and static and electric light scattering, to determine electrophoretic mobility, particle size, mass increment of MM nanoplates upon cytC adsorption, ratio of adsorbed to free cytC, and number of cytC globules adsorbed on a single MM monoplate, as well as computer techniques to analyze the electric charge and potential of cytC globules and organization of the protein monolayer on MM surface. The observed protein concentration dependence of the mass increment discloses a positive cooperative effect and formation of cytC monolayer on MM surface at saturated adsorption. In vitro experiments with a colon cancer cell culture exhibit an exponential correlation of the cytotoxicity with the concentration of cytC-MM particles in the suspension, which reaches 97% cell death after a 96-h period, but neither cytC solution nor MM suspension exhibited any noticeable effect on tumor cells. The suspension of cytC-MM nanoplates demonstrated high cytotoxic effectivity and has potential application in the anticancer treatment of superficial neoplasms of the skin and gastrointestinal tract.