Recent progress in surface forces measurements allow us to measure forces between protein adsorbed mica surfaces directly. The force curves can be devided into two regimes due to the surface separation, a “longer distance” regime and an “adsorbed layer” regime. In a “longer distance” regime, the forces are largely due to an electrostatic double-layer force originating from the charges on the adsorbed protein layers. In the “adsorbed layer” regime, forces of steric origin owing to overlap of adsorbed layers dominate. From the analysis of the forces in an “adsorbed layer” regime, conformations of the adsorbed protein molecules can be estimated.