Though emerging evidence indicates that the pathogenesis of Parkinson's disease is strongly correlated to the accumulation(1,2) and transmission(3,4) of alpha-synuclein (alpha-syn) aggregates in the midbrain, no anti-aggregation agents have been successful at treating the disease in the clinic. Here, we show that graphene quantum dots (GQDs) inhibit fibrillization of alpha-syn and interact directly with mature fibrils, triggering their disaggregation. Moreover, GQDs can rescue neuronal death and synaptic loss, reduce Lewy body and Lewy neurite formation, ameliorate mitochondrial dysfunctions, and prevent neuron-to-neuron transmission of alpha-syn pathology provoked by alpha-syn preformed fibrils(5,6). We observe, in vivo, that GQDs penetrate the blood-brain barrier and protect against dopamine neuron loss induced by alpha-syn preformed fibrils, Lewy body/Lewy neurite pathology and behavioural deficits.