Group A Streptococcus (GAS) consists of a vast variety of virulence factors that help the bacterium from evading its host’s immune response, making it a relatively successful pathogen. Spy0433, one of the uncharacterized GAS proteins, was found to bind a few innate immune components including complement 1 subcomponent subunit C (C1qC) and myeloperoxidase (MPO), postulating its potential as an immune evasion factor. To investigate the functional effect of these interactions, Wieslab complement system screen, chlorination, and peroxidation assays were performed. The interactions of Spy0433 with plasma proteins and leukocytes were respectively examined via pull-down assay and flow cytometry. Western blot was also carried out to identify the expression of Spy0433 during the course of GAS infection. Spy0433 was shown to inhibit the chlorination activity of MPO that has an antimicrobial effect, where it reached nearly 100% inhibition at 15.27 µM. The protein also specifically binds granulocytes and monocytes that play an important role in innate immunity. However, no inhibition of Spy0433 was detected against the three complement pathways. The protein did not bind to any plasma proteins in the pull-down assay. The result for Western blot was inconclusive to confirm that Spy0433 was expressed during GAS infection. Overall, my project displayed that Spy0433 is an MPO inhibitor with a possible evasion mechanism against the innate immune cells.