Abstract: 24 male piglets were divided into 3 groups randomly: control group (weaning in 28 day’s old) , ExperimentalⅠgroup (feeding with 10 μmol/L β-CM-7 group) and ExperimentalⅡ group (casein hydrolysate group ). Experimental groups were weaned in 21 days and fed with casein hydrolysate and β-CM-7( 2 times every day, 10 mL every time ). On 32 days, 6 chosen piglets from each group were killed for determination of stomach , jejunum digesta and blood CMs.The result showed that there were β-CM-5 and β-CM -7 in stomach and jejunum digesta, average content of β-casomorphin-7 were 21.12±2.38, 23.58±7.49, 21.81±9.93 μg/g stomach digesta and 16.99±3.48, 19.08±2.85 and 21.36±4.85 μg/g jejunum digesta, respectively. The concentration of CMs in stomach was higher and two Experimental groups were more than control group. Compared with control group (normal weaning group), other two groups which fed with β-CM-7 or casein hydrolyates inhibited adenylate cyclase activity of NG108-15 hybrid tumor cell and decreased the intracellular level of cAMP. The ratio of the inhibitions were 27.9% and 89%, and were reversed 43.2% and 89.07% by naloxone. The results indicted that CMs were released by feeding β-CM or casein hydrolysate, and can enhance opioid activity in gutgastric tract of 21 days’ weaning piglets.