There have been numerous studies on measuring protein-protein interactions in solution using a variety of techniques including membrane osmometry, sedimentation, and static light scattering. Most of these techniques yield an osmotic second virial coefficient. The osmotic second virial coefficient has been shown to be an important parameter for protein crystallization. To date, there have been few fundamental theoretical studies of estimating second virial coefficient values using conventional models because of the diverse and complex nature of the potential of mean force. In the present study, the variation of equine serum albumin interactions was measured with respect to pH and sodium chloride salt concentration by static light scattering to determine the second virial coefficient and electrophoretic light scattering to determine the electrophoretic mobility. The main aim is to show the effect of the solution conditions such as pH and ionic strength on ESA interactions. In this thesis, I will focus on the classical theory of Derjaguin, Landau, Verwey and Overbeek (DLVO). The experimental data from electrophoretic and static light scattering measurements for equine serum albumin are compared with the DLVO model.