The pathological hallmark of many neurodegenerative diseases is the accumulation of characteristic proteinaceous aggregates. Parkinson's disease and dementia with Lewy bodies can be characterized as synucleinopathies due to the abnormal accumulation of the protein alpha-synuclein (α-Syn). Studies have shown amyloidogenic proteins such as α-Syn and tau can exist as polymorphic aggregates, a theory widely studied mostly in their fibrillar morphology. It is now well understood that an intermediate state of aggregates, oligomers, are the most toxic species. We have shown α-Syn, when modified by different physiological inducers, result in distinct oligomeric conformations of α-Syn. Polymorphic α-Syn oligomers exhibit distinct properties such as aggregate size, conformation, and differentially interact with tau. In this study, we confirm α-Syn oligomeric polymorphs furthermore using in-house novel α-Syn toxic conformation monoclonal antibodies (SynTCs). It is unclear the biological relevance of α-Syn oligomeric polymorphisms. Utilizing a combination of biochemical, biophysical, and cell-based assays, we characterize α-Syn oligomeric polymorphs. We found α-Syn oligomeric polymorphs exhibit distinct immunoreactivity and SynTCs exhibit differential selectivity and binding affinity for α-Syn species. Isothermal titration calorimetry experiments suggest distinct α-Syn:SynTC binding enthalpies in a species-specific manner. Additionally, we found SynTCs differentially reduce α-Syn oligomeric polymorph-mediated neurotoxicity and propagation in primary cortical neurons in a polymorph-specific manner. These studies demonstrate the biological significance of polymorphic α-Syn oligomers along with the importance of polymorph-specific antibodies that target toxic α-Syn aggregates. Monoclonal antibodies that can target the conformational heterogeneity of α-Syn oligomeric species and reduce their mediated toxicity have promising immunotherapeutic potential.