Abdominal surgery may affect intestinal absorption and the resulting levels of posaconazole in the blood. We measured plasma posaconazole levels in surgical intensive care unit (SICU) patients and tried to develop a predictive population pharmacokinetics model. A total of 270 samples from 15 patients receiving posaconazole via nasogastric tube were measured by high-performance liquid chromatography (HPLC). SICU patients showed lower plasma drug concentrations, a higher apparent clearance, and a higher volume of distribution than those in hematology patients, possibly due to poor absorption.