Zwitterionic polymers are widely employed hydrophilic building blocks for antifouling coatings with numerous applications across a wide range of fields, including but not limited to biomedical science, drug delivery and nanotechnology. Zwitterionic polymers are considered as an attractive alternative to polyethylene glycol because of their enhanced biocompatibility and effectiveness to prevent non-specific protein adsorption and formation of biofilms. To this end, zwitterionic polymers are classified in two categories, namely polybetaines and polyampholytes. Yet, despite a fundamental interest to drive the development of new antifouling materials, the chemical composition of zwitterionic polymer remains severely limited. Here, we propose an entirely new class of antifouling polymers, namely poly(sulfur ylides) belonging to the largely overlooked class of poly(ylides). We show that poly(sulfur ylides) effectively prevent the adhesion of biomolecules and formation of biofilms from pathogenic bacteria. While surface energy analysis reveals strong hydrogen-bond acceptor capabilities of poly(sulfur ylide) and suggests a repellent hydration barrier, membrane damage of pathogenic bacteria induced by poly(sulfur ylides) indicates a killing-by-contact mechanism. Such synergistic effect of poly(sulfur ylides) offers distinct advantages over polyethylene glycol when designing antifouling materials in the future. We expect that our findings will pave the way for the development of a range of ylide-based materials with antifouling properties that have yet to be explored, opening up new innovative directions at the interface of chemistry, biology, and material science.