Quantum dots (QDs) have been used as a new class of bioprobes in medical imaging in recent years. The study of interaction between QDs and biomacromolecules is important for interpreting biological data. In this work, Rayleigh light scattering (RLS) was employed to investigate the nonspecific interaction between mercaptoacetic acid modified CdSe/ZnS quantum dots (MAA-QDs) and human immunoglobulin G (IgG). The conjugation processes between QDs and IgG in different conditions including addition sequence, pH were carefully studied. The addition of IgG to QDs solution was found to form a fixed size of QDs-IgG conjugate, with the QDs-to-IgG ratio of approximately 13, while the addition of QDs to IgG solution resulted in a gradually increased conjugate size, with variable QDs-to-IgG ratio till the binding saturation was reached.