The study was undertaken to evaluate the effect of major blood components on the CT number. The CT numbers according to the various levels of hematocrit, total protein and cholesterol were checked and analyzed by the dilution of pack cell, plasma and 184 complete blood cell count samples under same scanning conditions. In case of normal protein and cholesterol level (33 samples), the CT number was increased about 5.5 hounsfield unit according to 10% increase of hematocrit level: and In case of normal hematocrit and cholesterol level(39 samples), the CT number was increased about 3.5 hounsfield unit according to 1gm% increase of protein level. CT number changes were not predictable according to the changes of cholesterol level(34 samples). From these results, we concluded that major blood component should be considered in the CT number analysis of tissue.