Objective To investigate the roles of serum soluble Fas (sFas) and soluble Fas ligand (sFasL) in the development and progression of Parkinson's disease (PD).Methods Sixty patients with PD (26 females and 34 males) were selected as study group, and 30 healthy subjects (14 females and 16 males) were selected as control group. Enzyme-linked immunosorbent assay was used to measure serum levels of sFas and sFasL in both groups, and the differences in sFas and sFasL concentrations between the two groups were evaluated.Results All patients with Hoehn-Yahr stage 1-5 PD had significantly higher serum levels of sFas and sFasL than the control group (P<0.05 for all). Patients with mild, moderate, and severe PD, as evaluated according to the UPDRS scoring system, had significantly higher serum levels of sFas and sFasL than the control group (P<0.05 for all). In PD patients, serum levels of sFas and sFasL were positively correlated with each other (r=0.801, P=0.01).Conclusions Serum levels of sFas and sFasL are positively correlated with the severity of PD. sFas and sFasL might play an important role in the pathogenesis of PD.