Contribution of surface functional groups and detailed interface interaction for biosorption of strontium ions by Saccharomyces cerevisiae under culture conditions was investigated through chemical modification, in addition to spectroscopic and mesoscopic methods. The results showed that the biosorption ratio decreased approximately 10%, 60%, and 70% for ester group, carboxyl group, and amino group modified yeast cells, respectively. Fourier transform infrared spectroscopy and surface functional group potentiometric titration results revealed that –NH₂, –COOH, and –OH were the major binding groups. The amino group displayed the greatest contribution to biosorption of strontium ions, followed by the carboxyl group and, finally, the ester group. Electrostatic interaction was the initial role and establishment of a coordination complex was the most common mechanism of interface interaction between strontium ions and the yeast cell surface. Mesoscopic analysis suggested that strontium ions may be first adsorbed on the cell surface and then transported into the cytoplasm. Transmembrane transport and the bioaccumulation model revealed that yeast cells may regulate the distribution of strontium ions through a transportation mechanism. A detailed interface interaction was discussed for S. cerevisiae biosorption of low concentration strontium ions under culture conditions. The results suggested that optimal biosorption for a microorganism relies upon enrichment of proteins and polysaccharides on the cell surface.