CdSe nanocrystals (NCs) that show an excellent photoluminescence (PL) attract much attention owing to their promising applications in LED. They are usually coated by the wider band materials such CdS and ZnS in order to improve the quantum yield with the chemical resistance. However, the relationship between optical property and structure is not clarified, because the evaluation of core/shell structure is difficult. The common evaluation of optical property that is conducted as a collectivity such as UV-vis absorbance has some uncertainty, because the morphology of individual NC is not complete same and the property would be not also same. In this study, we have tried to direct-evaluate the optical properties and structure of individual single NCs. Even the optical properties from UV to NIR can be evaluated by the HR-EELS (Low-loss region) using the monochromator TEM. We have discussed the optical and structure property by the comparison of above evaluation and HR-STEM analysis.