Brucella and Mycobacterium tuberculosis (MTB) primarily affect the spine and only rarely the knee joint in osteoarticular disease in adults. We present an unusual instance of brucellar knee arthritis combined with knee joint tuberculosis. A 59-year-old man was initially diagnosed with brucellar knee arthritis in the orthopedics department of our hospital, while two weeks of standardized treatment did not improve the joint discomfort and inflammation indexes. Subsequent evaluation of serum tuberculosis interferon-gamma release assays (TB-IGRAs) and the effectiveness of empirical anti-tuberculosis therapy confirmed the mixed infection of tuberculosis. This case report demonstrates that clinical signs and imaging for brucellar knee arthritis and knee joint tuberculosis are similar. Patients with both disorders are more likely to be misdiagnosed or have their diagnosis delayed; clinicians should be aware of this uncommon combination of mixed infections.