The adsorption of native, wild-type, and engineered cytochrome c on sodium-exchanged kaolinite was investigated by spectroscopic means. The variants of yeast cytochrome c were obtained replacing surface lysines in positions 72, 73, and 79 with alanine residues. All proteins are strongly adsorbed onto kaolinite. In particular, the presence of the lysine residue in position 73 remarkably favors adsorption. A detailed characterization of the thermodynamic aspects of the adsorption process has been performed. Most notably, adsorbed cytochrome c maintains its moderate peroxidase activity against guaiacol. This investigation is prodromal to the exploitation of the catalytic activity of engineered cytochrome c immobilized on a polydisperse system.