Objective: The aim of the present study was to evaluate the stability of native bovine ? casomorphin 7 in duodenum of adult rats, and the local effect on expression of cholecystokinin in intestinal mucosa. Method: (1) According to the variety of infused ? casomorphin 7 concentrations between absorptive and un-absorptive groups in vivo, its characteristic absorption in duodenum was observed. (2) To characterize the stability of the ? casomorphin 7, rat intestinal mucosa homogenate was digested and the enzyme activities were determined in vitro. (3) The effect on cholecystokinin mRNA expression of ? casomorphin 7 after luminal administration was analyzed by RT-PCR. Results:? casomorphin 7 was unable to be absorbed by intestinal epithelia and quickly degraded in the intestinal tract. It contributed to elevate cholecystokinin mRNA expression in intestinal mucosa and this effect was partly blocked by naloxone. This peptide also significantly inhibited the somatostatin mRNA expression. Conclusion: The present data demonstrated that the local effect on expression of cholecystokinin of ? casomorphin 7 might be related to opioid system and directly or indirectly affected by somatostatin.