The paper focused on the effect of microecological preparation on the growth performance and immunoreactive cells of 5-HT in hypothalamus-pituitary-adrenal (HPA) axis of rabbits. One hundred and eight male weaned rabbits were randomly divided into 4 groups. Control group was fed the basal diet. Probiotics group was fed the diet supplemented with 0.1% Bacillus cereus PAS38. Prebiotics group was fed the diet with 0.2% mannan. Synbiotics group was fed the diet supplemented with 0.1% B.cereus PAS38 and 0.2% mannan. Forty eight rabbits (12 rabbits in each group with 3 replicates and 4 rabbits in each replicate) were selected to observe the growth performance. In the other 60 rabbits, 5 rabbits from each group were slaughtered at 60 d, 75 d and 90 d of age, respectively. Immunohistochemistry SABC was used to measure 5-HT of immunoreactive cells and the expression in HPA axis of rabbits. The results showed that the weight and average daily weight gain in probiotics group and synbiotics group were strongly significantly higher than those of the control group (P<0.01). The prebiotics group was significantly higher than that of the control group (P<0.05). F/G of probiotics, prebiotics and synbiotics group decreased 13.8%, 10.9%, 14.9% compared with the control group, respectively (P>0.05). The probiotics and prebiotics could not significantly change the number of immunoreactive cells of 5-HT in HPA axis of rabbits (P>0.05). At the 75 d and 90 d of age, the expression of 5-HT in HPA axis of the probiotics group and the synbiotics group were significantly (P<0.05) or strongly significantly (P<0.01) higher than that of the control group. The expression of 5-HT in HPA axis of the prebiotics group was significantly (P<0.05) higher than that of the control group at the 90 d of age. The results indicated that the microecological preparation could promote the growth and enhance the expression of 5-HT in HPA axis of rabbits.［Chinese Journal of Animal Nutrition, 2009，21(6):945-952］