Objective To reveal the laws of human intestinal tract adapting seasonal and climate changes and provide invidence for TCM theory of correspondence between nature and human through observing different levels of interleukin-2 (IL-2) in rat jejunum, ileum and colon in five seasons of Chinese medicine. Methods Pinealectomized rat model was taken as study object, and the changes of IL-2 levels in rat jejunum, ileum and colon in five seasons (spring, summer, latter summer, autumn and winter) and changes after pinealectomizing were observed. Results In normal group, the level of IL-2 was higher in jejunum in latter summer compared with other 4 seasons (P < 001), higher in latter summer and winter in ileum compared with spring, summer and autumn (P < 0. 01 or P < 0. 05) and higher in colon in winter compared with other 4 seasons (P <0. 01). After pinealectomizing, the normal seasonal and climate rhythm of IL-2 secretion was disorder in all intestinal sections. Conclusion The level of IL-2 has seasonal and climate changes in rat jejunum, ileum and colon, which is consistent with TCM theory of correspondence between nature and human. The pineal gland takes part of the rhythmic regulation of intestinal function.