The pathological hallmark of Parkinson's disease (PD) is loss of dopaminergic neurons in the substantia nigra and the presence of Lewy bodies, which are composed of α-synuclein (αSYN) fibrils. Recently, mutations in vacuolar protein sorting 35 (VPS35) have been identified as a cause for the rare familial form of PD. VPS35, a key component of the retromer, mediates retrograde transport of cargo proteins from the endosome to the trans-Golgi network. To investigate the functional roles of retromer in the pathogenesis of PD, RNAi-mediated silencing of VPS35 was performed using cellular and in vivo human wt-αSYN-expressing Transgenic fly models. We showed that the silencing of VPS35 in cultured cells caused an increase in the lysosomal turnover of the cation-independent mannose 6-phosphate receptor, thereby affecting the trafficking of CTSD, a lysosome protease involved in αSYN degradation. VPS35 knockdown perturbed the maturation step of cathepsin D in parallel with the accumulation of αSYN in the lysosomes. Co-expression of siRNA resistant-wt VPS35 rescued αSYN degradation in VPS35 siRNA-treated cells. Furthermore, RNAi-mediated knockdown of Drosophila melanogaster VPS35 not only induced the accumulation of detergent-insoluble αSYN species in the brain but also exacerbated both compound eye degeneration and locomotor impairments in the flies expressing the human wild-type αSYN. Together, our results provide evidence that retromer plays a crucial role for αSYN catabolism by modulating the processing of lysosomal protease CTSD and would thereby contribute to the disease pathology linked to PD.