Early weaning is desired in dairy production as it lowers production cost. The objective of this study was to evaluate how weaning age affect the development of ruminal microbiota using lambs as a model. Ten 5-d-old male Hu lambs weighing 3.6 ± 0.37 kg each were randomly assigned to 2 weaning age groups: early weaning (EW) at d 30 or normal weaning (NW) at d 45, with 5 lambs in group. All lambs had colostrum within 4 h after birth, and they were subjected to a 5-d adaptation to a milk replacer (MR; 18.4% CP, 13% CF). Starter (16% CP, 10.9 MJ/kg ME) and Chinese wild rye were fed ad libitum from d 10 on. To stimulate intake of solid feed, MR was given at 780 mL/d (based on consumption in the adaptation period) at d 11 and was then reduced at a rate of 30 mL/d until reaching 210 mL/d, which was the rate given until the weaning age. The lambs were then slaughtered to obtain the rumen content samples for analysis for volatile fatty acids (VFA) using gas chromatography and rumen microbiota using metagenomics. Data were analyzed by one-way ANOVA using GLM of SAS. The results showed that the early weaning had no effect on total VFA concentration (1.58 vs 2.50 mg/g; P > 0.05) but decreased the acetate (53.0 vs 69.2 mM/100 mM; P < 0.05) while increasing propionate (45.0 VS 29.5 mM/100 mM; P < 0.05) molar proportion. The major phyla of the rumen microbiota included Firmicutes, Bacteroidetes, Actinobacteria, Proteobacteria, and Fibrobacteres irrespective of the weaning age. The EW group had a greater relative abundance of Bacteroidetes and Proteobacteria than the NW group (P < 0.05), but a lower relative abundance of Actinobacteria (P < 0.05). At the genus level, Prevotella was the most predominant. Compared with the NW group, the early weaning significantly increased the relative abundance of Prevotella, Bacteroides, Succinivibrio, Clostridium IV, Dialister, and Fibrobacter(P < 0.05) while decreasing that of Olsenella, Bifidobacterium, Ruminococcus and Selenomonas. Early weaning could increase the propionate molar proportion and change the rumen bacterial communities, which may have beneficial effect on the rumen development of Hu lambs.