Ag Te quantum dots (QDs) have attracted great attention in biological applications due to their superior photoluminescence qualities and good biocompatibility, but their potential biotoxicity at a molecular biology level has been rarely discussed. In order to better understand the basic behavior of Ag Te QDs in biological systems and compare their biotoxicity to cadmium-containing QDs, a series of spectroscopic measurements was applied to reveal the molecular interactions of Ag Te QDs and CdTe QDs with human serum albumin (HSA). Ag Te QDs and CdTe QDs statically quenched the intrinsic fluorescence of HSA by electrostatic interactions, but Ag Te QDs exhibited weaker quenching ability and weaker binding ability compared with CdTe QDs. Electrostatic interactions were the main binding forces and Sudlow's site I was the primary binding site during these binding interactions. Furthermore, micro-environmental and conformational variations of HSA were induced by their binding interactions with two QDs. Ag Te QDs caused less secondary structural and conformational change in HSA, illustrating the lower potential biotoxicity risk of Ag Te QDs. Our results systematically indicated the molecular binding mechanism of Ag Te QDs with HSA, which provided important information for possible toxicity risk of these cadmium-free QDs to human health.