Rhizobium radiobacter is an aerobic, gram negative, rod-shaped, bacterium typically found in the soil. Commonly a plant pathogen, it is also a rare human pathogen causing serious disease. Risk factors for infection include neutropenia, leukopenia, catheters, hospitalization, and low CD4+ lymphocyte count, especially in patients with malignancy or human immunodeficiency virus. There is currently limited literature to establish a definitive guideline for antimicrobial therapy and obtaining susceptibilities from a specialized laboratory is appropriate. We present a successfully treated case of R. radiobacter bioprosthetic mitral valve endocarditis in a patient with previous S. epidermidis endocarditis.