Autophagy is a catabolic process that allows cellular macromolecules to be broken down and recycled as metabolic precursors. The influence of non-coding microRNAs in autophagy has not been explored in colon cancer. In this study, we discover a novel mechanism of autophagy regulated by hsa-miR-502–5p (miR-502) by suppression of Rab1B, a critical mediator of autophagy. A number of other miR-502 suppressed mRNA targets (for example, dihydroorotate dehydrogenase) are also identified by microarray analysis. Ectopic expression of miR-502 inhibited autophagy, colon cancer cell growth and cell-cycle progression of colon cancer cells in vitro. miR-502 also inhibited in-vivo colon cancer growth in a mouse tumor xenografts model. In addition, the expression of miR-502 was regulated by p53 via a negative feedback regulatory mechanism. The expression of miR-502 was downregulated in colon cancer patient specimens compared with the paired normal control samples. These results suggest that miR-502 may function as a potential tumor suppressor and therefore be a novel candidate for developing miR-502-based therapeutic strategies.