Aggregation of α-synuclein (α-Syn) triggers development of α-synucleinopathies such as Parkinson’s disease and Dementia with Lewy Bodies. It also has known that α-Syn can spread in the whole brain, like as prions. However, the molecular mechanisms remain unclear. Here, we show that RNA G-quadruplexes (G4RNAs) promote α-Syn aggregation through liquid-liquid phase separation (LLPS). Electrophoretic mobility shift assay revealed that α-Syn significantly and preferentially formed a complex with G4RNAs than with mutated G4RNAs that is unable to form G4 and other structural RNAs (hairpin and polyA). α-Syn undergoes LLPS, and G4RNAs significantly facilitate liquid-to-solid transition of α-Syn under the condition of molecular crowding (15% polyethylene glycol). These observations suggest that α-Syn may undergoes phase transition by G4RNAs under the pathological condition in vivo. We would like to also discuss the role of G4RNA in α-Syn propagation in the meeting.