Abstract Purpose: Perineural invasion is associated with the high incidence of local recurrence and a dismal prognosis in pancreatic cancer. We previously reported a novel perineural invasion model and distinguished high– and low–perineural invasion groups in pancreatic cancer cell lines. This study aimed to elucidate the molecular mechanism of perineural invasion. Experimental Design: To identify key biological markers involved in perineural invasion, differentially expressed molecules were investigated by proteomics and transcriptomics. Synuclein-γ emerged as the only up-regulated molecule in high–perineural invasion group by both analyses. The clinical significance and the biological property of synuclein-γ were examined in 62 resected cases of pancreatic cancer and mouse models. Results: Synuclein-γ overexpression was observed in 38 (61%) cases and correlated with major invasive parameters, including perineural invasion and lymph node metastasis (P < 0.05). Multivariate analyses revealed synuclein-γ overexpression as the only independent predictor of diminished overall survival [hazard ratio, 3.4 (95% confidence interval, 1.51-7.51)] and the strongest negative indicator of disease-free survival [2.8 (1.26-6.02)]. In mouse perineural invasion and orthotopic transplantation models, stable synuclein-γ suppression by short hairpin RNA significantly reduced the incidence of perineural invasion (P = 0.009) and liver/lymph node metastasis (P = 0.019 and P = 0.020, respectively) compared with the control. Conclusions: This is the first study to provide in vivo evidence that synuclein-γ is closely involved in perineural invasion/distant metastasis and is a significant prognostic factor in pancreatic cancer. Synuclein-γ may serve as a promising molecular target of early diagnosis and anticancer therapy.