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α-Synuclein (α-syn) fibrillar aggregates are the major component of Lewy bodies and Lewy neurites presenting as the pathology hallmark of Parkinson’s disease (PD). Studies have shown that α-syn is potential to form different conformational fibrils associated with different synucleinopathies, but whether the conformation of α-syn fibrils changes in different phases of related diseases is to be explored. Here, we amplified α-syn aggregates from the cerebrospinal fluid (CSF) of preclinical (pre-PD) and late-stage postmortem PD (post-PD) patients. Our results show that compared to the CSF of pre-PD, that of post-PD is markedly stronger in seeding in vitro α-syn aggregation, and the amplified fibrils are more potent in inducing endogenous α-syn aggregation in neurons. Cryo-electron microscopic structures further reveal that the difference between the pre-PD- and post-PD-derived fibrils lies on a minor polymorph which in the pre-PD fibrils is morphologically straight, while in the post-PD fibrils represents a single protofilament assembled by a distinctive conformation of α-syn. Our work demonstrates structural and pathological differences between pre-PD and post-PD α-syn aggregation and suggests potential alteration of α-syn fibrils during the progression of PD clinical phases.Significance StatementIncreasing evidence support different conformational α-syn fibrils in patients with different α-synucleinopathies, but whether the conformation of α-syn fibrils changes in different phases of related diseases is unknown. Here, we show that α-syn fibrils amplified from the cerebrospinal fluid (CSF) of the late-stage postmortem PD (post-PD) patient are more potent in inducing endogenous α-syn aggregation in neurons than that amplified from the preclinical (pre-PD) patient. Cryo-EM structures further reveal that the post-PD fibrils contain a novel conformation that is distinct from either the pre-PD fibrils or those previously reported. Our work suggests conformational evolution of α-syn fibrils along with PD progression.