The experiment was conducted to study the effects of oligosaccharides on rumen microflora of weanling lambs. Forty F2 generation weanling lambs of Dorset with similar age and body weight were randomly allotted into 4 groups with 10 replicates per group and 1 lamb per replicate. The 4 groups were control group (basal diet), isomalto-oligosaccharide (IMO) group (basal diet+0.3% IMO), fructo-oligosaccharide (FOS) group (basal diet+0.3% FOS) and mixed oligosaccharides group (basal diet+0.3% IMO+0.3% FOS), respectively. The experiment lasted for 42 d (7 d for adaptation and 35 d for test). Diversity of rumen microflora was determined based on V6 to V8 variable regions of bacteria 16S rRNA by using denaturing gradient gel electrophoresis (DGGE) technique. The number of total bacteria, R. flavefaciens and F. succinogenes in the rumen was quantified by real-time quantitative PCR. The results showed as follows: compared with the control, the FOS significantly decreased the diversity of rumen microflora (P<0.05), but the diversity of rumen microflora was not affected by the IMO and mixed oligosaccharides (P>0.05); the FOS and IMO significantly decreased the number of bands in DGGE gel (P<0.05), while the number of bands in DGGE gel was not affected by the mixed oligosaccharides (P>0.05). The number of total bacteria (P<0.05), R. flavefaciens (P<0.05) and F. succinogenes (P>0.05) in rumen was increased by the FOS, while the number of F. succinogenes was significantly decreased by the IMO and mixed oligosaccharides (P<0.05). In conclusion, oligosaccharides can change the configuration of rumen microflora of weanling lambs, and the FOS can increase the number of total bacteria, R. flavefaciens and F. succinogenes in rumen.［Chinese Journal of Animal Nutrition, 2010，22（5）:1396-1401］