Brucellosis is a systemic infectious disease with a broad spectrum of clinical manifestations. It may go unnoticed, particularly in the areas with low incidence. Osteoarthicular manifestations are often seen in brucellosis but most of brucellar monoarthritis cases are reactive rather than being septic. Here we report the clinical manifestation, diagnosis and treatment of a case of brucellar septic monoarthritis of the knee joint.