Background and purpose: Recently, the number of patients with nonalcoholic fatty liver disease (NAFLD) has been increasing, and some of them progresses to cirrhosis and hepatocellular carcinoma. Dual energy CT allows the discrimination of substance using monochromatic image (MI), and steatosis exhibit specifically the CT value of each energy level. The purpose is to evaluate the fat quantification in the liver using spectral HU curve and CT value compare to a conventional image diagnosis. Methods: Dual energy CT and liver biopsy were performed in 54 patients between October 2014 and April 2016. The CT value of 40 keV MI was measured by spectral HU curve setting 3 points ROI on the right and left liver. The CT value of 40 keV MI was compared with steatosis area and the NAFLD activity score (NAS). Additionally, steatosis area was compared with the conventional CT value scan and hepatorenal echo contrast value. Results and discussion: The CT value of 40 keV MI exhibited a negative correlation for the stenosis area (R²=0.619), and NAS (R²=0.147). Steatosis area exhibited correlation for the conventional CT value (R²=0.407), and hepatorenal echo contrast (R²=0.135). This study suggests that the evaluation of the fat quantification in the liver using the spectral HU curve and CT value improved in comparison to the conventional image diagnosis.