The effects of Enterococcus faecium on growth, intestinal barrier function, and immune response in Escherichia coli O78-challenged broiler chickens were investigated. Three hundred eight 1-day-old Ross male chickens were randomly assigned into three treatment groups: negative control (C), E. coli O78-infected positive (EP), and E. coli O78-infected with 200 mg/kg E. faecium dietary supplementation (EF). E. faecium significantly increased the body weight on day 10 (P < 0.05) and day 15. Furthermore, these birds had a greater average daily gain compared with the other groups during days 1-10 (P < 0.05). The death rate of the EF chickens dramatically declined. E. faecium supplementation improved the jejunal villus height and the ratio of villus height to crypt depth (P < 0.05) 3 and 7 days post-infection. The mRNA expression of claudin-1 significantly increased by E. faecium (P < 0.05) 3 and 7 days post-infection, and Mucin2 was markedly enhanced (P < 0.05) 3 days post-infection. E. faecium upregulated the mRNA expression of PPAR-γ and IL-10 (P < 0.05) and downregulated that of NF-κB, TLR4, and IL-1β (P < 0.05) in the spleen 3 and 7 days post-infection. Lipopolysaccharide stimulation index was markedly enhanced in the EF group (P < 0.05) 3 days post-infection. The increased liver E. coli number caused by the E. coli O78 challenge was significantly reversed by E. faecium (P < 0.05). E. faecium improved growth and reduced the death rate by regulating the immune response and maintaining the intestinal integrity in E. coli O78-challenged broiler chickens.