A 69-year-old man consulted a local doctor because of a chief complaint of fever and anorexia. CT showed a giant liver mass of the right hepatic lobe and multiple pulmonary nodules. The patient was admitted to our hospital. We punctured the liver mass, obtaining pus, and as gram-negative bacilli were detected from both blood and pus cultures, a liver abscess with septic pulmonary embolism was diagnosed. Following a positive string test, we identified the pathogenic bacteria as hypermucoviscous Klebsiella pneumoniae, which is highly invasive to the tissues. The patient showed improvement following the administration of an antimicrobial agent (Meropenem) and multiple abscess drainage procedures.