Polyoxometalates (POMs) are nanometric metal−oxide anions with an unmatched range of chemical and physical properties. During the past decade, significant efforts have been made to study POM surface activity and self-assembly properties that are essential for catalysis applications and for producing organic−inorganic hybrid materials. A previous work highlighted the tungstosilicate (SiW12O404−) and tungstophosphate (PW12O403−) Keggin POM anions' spontaneous and noncovalent adsorption at the micellar surface of non-ionic surfactants. In this study, the critical micelle concentrations (CMC) of two non-ionic surfactants, the n-octyl-β-glucoside (C8G1) and the tetraethylene glycol monooctyl ether (C8E4), were measured in the presence of POMs, and we propose herein thermodynamic models to explain an increase or a decrease of the CMC depending on the choice of the POM/surfactant couple.