An analytical expression for the structure factor for globular proteins in aqueous solution is presented. This expression was obtained considering a potential given by the sum of a hard core, a van der Waals attractive, and a screened Coulomb contribution. Experimental data of small angle x-ray scattering for bovine serum albumin (BSA) in aqueous solutions containing sodium salts at different protein concentrations and pH values are also presented. The developed expression for the structure factor describes accurately these experimental data provided a dependence of the attractive parameter on protein concentration is established. An expression for the osmotic pressure was derived from the structure factor. With attractive parameters adjusted from x-ray scattering data, the osmotic pressure of BSA aqueous solutions could be predicted with very good agreement with experimental data. (c) 2015 American Institute of Chemical Engineers AIChE J, 61: 2871-2880, 2015