Background.α-Synuclein (SNCA) and microtubule-associated protein tau (MAPT) are the two major genes independently, but not jointly, associated with susceptibility for Parkinson’s disease (PD). TheSNCAgene has recently been identified as a major modifier of age of PD onset. WhetherMAPTgene synergistically influences age of onset of PD is unknown.Objective. To investigate independent and joint effects ofMAPTandSNCAon PD onset age.Methods. 412 patients with PD were recruited from the Australian PD Research Network (123) and the Neurology Department, Ruijin Hospital Affiliated to Shanghai Jiaotong University, China (289).MAPT(rs17650901) tagging H1/H2 haplotype andSNCA(Rep1) were genotyped in the Australian cohort, andMAPT(rs242557, rs3744456) andSNCA(rs11931074, rs894278) were genotyped in the Chinese cohort. SPSS regression analysis was used to test genetic effects on age at onset of PD in each cohort.Results.SNCApolymorphisms associated with the onset age of PD in both populations.MAPTpolymorphisms did not enhance such association in either entire cohort.Conclusion. This study suggests that, in both ethnic groups,SNCAgene variants influence the age at onset of PD andα-synuclein plays a key role in the disease course of PD.