Rab3D belongs to Rab protein family. Previous reports showed that the expression of Rab3D was dysregulated in various types of cancer. Rab3D belongsRab3D belongs. However, little is known about the role of Rab3D in carcinogenesis and progression of colorectal cancer (CRC). Here, we first evaluated the expression of Rab3D in 32 fresh CRC and matched normal tissues and found Rab3D was dramatically increased in CRC tissues compared to normal tissues (p<0.001). Furthermore, immunochemistry was used to investigate Rab3D expression in 300CRC tissue specimens. The expression of Rab3D significantly positively correlated with the tumor size (p=0.041), CEA level (p=0.007), tumor classification (p=0.030), lymphatic metastasis (p<0.001), distant metastasis (p=0.013) and clinical stage (p=0.003). We also demonstrated that overall survival is poor in CRC patients with high expression of Rab3D (p<0.001). Finally, we showed that Rab3D activated Akt/GSK3β/Snail pathway and induced EMT process in colorectal cancer cells. In conclusion, this study establishes increased Rab3D expression is associated with invasiveness of CRC cells, and Rab3D expression status may serve as a reliable prognostic biomarker in CRC patients.