In a prospective study of 32 IBD patients (8-21 years old) and 18 healthy individuals, the expression levels of clock genes (CLOCK, BMAL1, CRY1, CRY2, PER1, and PER2) were analyzed in the peripheral blood and intestinal mucosa samples, and the expression levels of clock genes (CLOCK, CRY1, CRY2, PER1, and PER2) in the inflamed intestinal mucosa of the patients were significantly lower than those of the control intestinal mucosa (P < 0.05). This evidence concerns the gene PER2 and inflammatory bowel disease.