The adsorption kinetics of ${eta}$-casein on a hydrophobic surface has been studied by means of the quartz crystal microbalance (QCM). The self assembled monolayer of 1-octadecanethiol on a gold coated quartz crystal was used as a hydrophobic surface for adsorption. The adsorption kinetics was monitored in different solution conditions. Formation of monolayer is observed in most cases. At high concentration of protein, micelle formation which is interrupted by high ionic strength of solution is observed. Casein binding cations such as $Ca^{2+},;Ba^{2+};and;Al^{3+}$ increase the hydrophobicity of the protein and the multiple layer adsorption occurs. The strong and weak points of the QCM method in the study of protein adsorption are discussed.