Abstract <p>The thermal stability of bovine serum albumin (BSA) was studied in the presence of three anionic sulfated polysaccharides, κ-, ι-, and λ-carrageenans, which differ in the number of sulfate groups linked to galactose units. The polysaccharides are able to form the complexes with both the globular and unfolded forms of BSA, primarily stabilized by electrostatic interactions. κ- and ι-carrageenans have a higher affinity for native than for unfolded BSA and promote an increase in its thermal stability. λ-Carrageenan carries a higher negative charge and shows stronger binding preferences for the unfolded form, which reduces the onset temperature of denaturation. The addition of 0.5 M sodium chloride increases the thermal stability of BSA itself and disrupts the complexes with the unfolded protein. Under these conditions, all three carrageenans become bound to the native form of BSA.</p>