In this study, we observed an up-regulation of PER2 in GC, an up-regulation of CRY1 in cancers of more advanced stage, and a correlation between patients’ survival days and the expression level of PER3. Our results suggest that deregulated expression of circadian clock genes exits in GC and that circadian rhythm disturbance may be associated with the development of GC. Here, PER3 is linked to cancer.