Here we report the adsorption behavior of protein at an oil-water interface, that is covered with polyelectrolytes (PE) and the interaction forces involved. The weak and strong PE’s used are poly(acrylic acid), PAA and poly(diallyldimethylammonium chloride), PDDA, respectively. The protein and oil used are bovine serum albumin (BSA) and octane droplets in water, containing superparamagnetic magnetite nanoparticles, respectively. The intermolecular forces, hydrodynamic diameter and electrophoretic mobility measurements are used to study the adsorption behavior of protein. The results showed an enhanced displacement of the adsorbed PDDA and PAA with increasing concentrations of BSA. In the absence of BSA, the emulsion droplets covered with PDDA and PAA exhibited a long range repulsive interaction. The addition of BSA into PDDA and PAA stabilized emulsion resulted in a decrease in the onset of interaction of repulsive force profile. The reversal of the sign and the change in the magnitude of zeta potential indicates the displacement of PDDA by BSA molecules at the oil-water (O/W) interface, which was in agreement with the findings of Satulovsky et.al. [Proc. Natl. Acad. Sci. 97 (2000) 9037–9041] that polymers on hydrophobic surfaces are not effective in preventing protein adsorption. These results indicate the displacement of macromolecule of very large molecular weight and preferential adsorption of small macromolecules at the O/W interfaces, irrespective of the nature of adsorbed PE’s (strong or weak, anionic or cationic with high or low charge density). These finding provides new insights into adsorption of proteins at the oil-water interfaces and may have important implication in tailoring industrial formulations with an extended shelf life and in increasing biocompatibility of implants.