The utilization of proper fermentation techniques is a widely recognized, efficacious approach in animal husbandry for enhancing the feed quality. However, research on vegetable waste, particularly that of roots, stems, leaves, fruits, and peels, has been rarely reported. To this end, the present study was carried out to examine the impact of vegetable leaf fermentation on growth performance, immune function, antioxidant levels, intestinal morphology, and microbial composition in sheep. Fifty-four male sheep (Oula) with an average age of 6 months and an average body weight of (21.53 ± 2.03) kg were randomly divided into three treatment groups, with six replicates each. The groups were fed with a basal diet (CON), 30% commercial fermented concentrate (CFC), and 30% vegetable leaf fermented concentrate (VFC). The results showed that compared to the CON group, both the commercial fermented concentrate and the vegetable leaf fermented concentrate improved the final weight (8.93%), average daily gain (30.67%), and dry matter intake of the sheep (1.62%). VFC increased the serum T-AOC (34.45%) and significantly increased the activities of serum and liver GSH-PX (10.95%). Meanwhile, the addition of vegetable leaf fermented concentrate increased the levels of serum IgA (63.21%), IgG (73.06%), and IgM (69.41%). VFC increased the villus height of the jejunum by 87.4% and the ileum by 185.5% and improved the villus height/crypt depth (V/C) ratio of the duodenum and ileum. CFC can also increase the villus height of the duodenum and jejunum, but has no effect on the morphology of the ileum. In addition to its other regulatory effects, VFC can further improve the richness and diversity of the rumen microbial community in sheep, with a notable enhancement in the relative abundance of key phyla, including Bacteroidetes, Ascomycota, Zygomycota, Chytridiomycota, and Basidiomycota. At the same time, the relative abundance of Succinivibrio was reduced. It can thus be concluded that the vegetable leaf fermented concentrate improves the growth performance and intestinal health of sheep.