Abstract:Ultrastructural observation of chloroplasts in different sections of young and mature leaves of Cymbidium sinense (Andr.) Willd. showed that the grana in chloroplasts of mature leaves were well developed, with tight thylakoid membrane. Osmiophilic granules in young leaves were few, whereas those in mature leaves were many, and so were the starch grains. In comparison with mature leaves, fewer grana, smaller chloroplasts and lower photosynthetic oxygen evolution rate were found in young leaves. In young leaves，chloroplasts in leaf apex were biggest，and in leaf base， smallest，but lower oxygen evolution rate was shown in leaf apex．No significant difference was found in chloroplast size and chlorophyll content among various parts of mature leaves．Chlorophyll content is not in direct proportion to oxygen evolution rate．