Determination of whether ion specific potassium halides binding with BSA occurred within the experimental conditions was the aim of the study. Ultrasound velocity measurements using a Resoscan system and density measurements using a DMA 5000M density meter were made to analyse BSA conformation in the presence of potassium salts of the Hofmeister series. It was found that the density and the adiabatic compressibility of BSA-potassium halide mixed aqueous solutions cannot be predicted from the density and the adiabatic compressibility of potassium halide solutions and that of BSA solutions. Interaction occurs between BSA and Br-, I- and F- ions in mixed aqueous solutions of BSA-KBr, BSA-KI and BSA-KF, but there is no interaction between BSA and Cl- ion in BSA-KCl mixed aqueous solution. The interaction of ion to BSA is ion non-specific to the Hofmeister series.