Serratia marcescens (S.M) is a species of gram–negative bacteria in the family enterobacteriaceae. A human pathogen, S. marcescens is involved in nosocomial infections, particularly in urinary tract and wound infections. This report describes a 63 years-old man that referred to hospital with dyspnea FC IV and he underwent cardiac valves replacement surgery with a diagnosis of severe mitral stenosis (M.S), severe tricuspid regurgitation (T.R), and moderate aortic insufficiency (A.I). Five days after operation, he presented with 40 °C fever, respiratory distress, elevation of liver enzymes, and decreased consciousness. Sepsis work up showed positive blood culture for Serratia marcescens. Despite therapy, he died due to Serratia marcescens endocarditis and mediastinitis. Positive blood culture for Serratia marcescens is very rare but it should be considered in post operation patients after cardiac valve replacement presenting with fever. Besides, prevention of endocarditis due to Serratia marcescens should be observed.