Supplementation of the starter diet with mannan-oligosaccharide or inulin had no effect on rabbit growth during the whole fattening period. Compared with control and MOS diet, the inulin addition remarkably affected the caecal microbial activity in a beneficial way, which lowered both the morbidity and health risk index of rabbits in the first weeks after weaning. No effect was detected on the mortality of rabbits. The results of our study suggest the importance of using inulin-type fructans in the nutrition of young rabbis. The higher health risk index of rabbis observed after change of diet indicates that prebiotics should be given for a longer time during the fattening period.