Objectives: Enterococcus faecium is a Gram-positive bacterium with evolving multi-drug resistance. It is one of the primary causes of urinary tract infections and endocarditis, among other opportunistic bacteria. The rise of antibiotic resistance in E. faecium makes treating its illnesses a significant therapeutic challenge. As a result, there is an urgent need for alternative treatments as well as preventive measures like vaccination. Previous research studies have suggested that the secreted antigen A (SagA) protein of E. faecium is a promising vaccine candidate. However, it was reported that capsular polysaccharides prevented the phagocytic activity of PMN to several E. faecium strains. Moreover, the surface accessibility of protein antigens was reported to be variable from one encapsulated strain to another. Methods: In this study, recombinant SagA was produced and investigated as a potential vaccine candidate against an encapsulated E. faecium isolate. Antibodies against SagA were raised in vivo and tested against E. faecium using ELISA and dot blot assay. Active immunization of mice using the recombinant SagA was performed, which was followed by a challenge with E. faecium. Results: Even though the ELISA and dot blot assay showed promising results, antibodies against SagA failed to be opsonic in the opsonophagocytic assay and failed to produce significant protection in an experimental mouse model against encapsulated E. faecium. Conclusion: The absence of protection despite the presence of significant antibody titer could be attributed to the existence of the capsule which might limit the surface exposure of the protein antigens and prevent the opsonophagocytosis in vivo.