We developed smaller sized quantum dots covered with sodium 2-mercaptoethanesulfonate which has a sulfonyl group (QDs-SO₃^–), and compared its stability in acid, salt and buffer solutions with that of the quantum dots covered with the mercaptoundecanoic acid (QDs-MUA) and covered with the NH₂ group (QDs-NH₂). We found that the QD-SO₃^– well disperses in these solutions without quenching and this stability holds on for 24 h. Next, we investigated the effect of Sheep Serum Albumin (SSA) coating. The SSA coating stabilizes the QD-MUA in the solutions. However, for the QD-SO₃^–, it does not have any significant effect. It implies that the QD-SO₃^– has advantages over the other quantum dots on the stability in the solutions. These results suggest that the novel surface processing using the sulfonyl group expands the possibilities of applications for various fields.