The major protein associated with Parkinson’s disease (PD) is α-synuclein, as it can form toxic amyloid- aggregates that are a hallmark of many neurodegenerative diseases. The biophysical and biochemical properties of α-synuclein can be modulated by a variety of post-translational modifications (PTMs). One prevalent modification that naturally occurs in vivo on α-synuclein is O-GlcNAcylation, the dynamic addition of β-N-acetyl glucosamine to the side chains of serine and threonine residues. Using synthetic protein chemistry, we have prepared α-synuclein bearing homogeneous O-GlcNAc modification at threonine 72, threonine 75, serine 81, serine 87, as well as a triply O-GlcNAc modified protein. We find that these synthetic proteins do not perturb membrane binding, an endogenous role of α-synuclein, but result in a dramatic inhibition in the formation of both oligomeric and fibrillar aggregates. Additionally, we show that O-GlcNAc modification inhibits protein aggregation in a hereditary form of PD (α-synuclein A53T). This data suggests that enhancing the levels of O-GlcNAc modification could be a viable treatment option for PD patients.