||Macromolecular interactions, mainly complexation and thermodynamic incompatibility, have been widely studied and in this study, self-assembly interaction between protein and polysaccharide is observed pH-dependent. Therefore, we carried out turbidity measurements at different pH to investigate the effect of ionic strength (0 to 100mM) on phase behavior of BSA/fucoidan which is known as bioactive and green material. Within the narrow pH range of 3.04.0, turbidity values were 2.75±0.01, 2.89±0.01 and 2.91±0.00 at pH 3.0, 3.5 and 4.0, respectively and complex coacervate was observed (Cp=0.6%, Pr:Ps=5:1). In this pH range, where both biopolymers were oppositely charged, complexation induced by electrostatic interactions. And increasing the ionic strength in the mixed system leads to dissociate the interaction between biopolymers due to ionic screening of salt ions on the molecular charges. In conclusion, the results seem to be adapted to the biomedical field.