In this study, the interaction of crebanine, an isoquinoline alkaloid, with immunoglobulin G (IgG) was evaluated. Subsequently, the anticancer effects of crebanine in MCF-7 breast cancer cells were assessed. The results demonstrate that static quenching plays a key role in the fluorescence quenching of the IgG by crebanine, and some embedded hydrophobic patches of the IgG are exposed upon interaction with crebanine, while the characteristic β-sheet conformation of the IgG was almost preserved. Theoretical studies also show that several hydrophilic and hydrophobic residues play a crucial role in the formation of hydrogen bonds between crebanine and IgG, along with the stability of the complex. Cellular studies indicate that crebanine induces selective anticancer effects in MCF-7 cells (IC