Abstract: In this paper we will represent the researches that we did on flue-cured tobacco cultivars including Hongda, K326, Yunyan87 and NC71 that were broadly planted in Yunnan province. Taking middle leaves of these cultivars that planted in the same field in mature period as test samples, we studied the relationships between the leaf’s stable carbon isotope composition（δ13C）and the ultrastructure of chloroplast, glandular hairs and stomas. The results were：(1) δ13C values were: K326＞NC71＞Hongda＞Yunyan87. (2)The average number of osmiophilic granules in chloroplasts was ranked as follows: K326＞NC71＞Hongda＞Yunyan87. (3) There were maximum and plumpest long-handled glandular hairs with secretory function on the surface of K326’s leaf while the Hongda’s is less and thinner. (4)The density of stomas was ranked as follows: K326＞NC71＞Yunyan87＞Hongda.（5）δ13C was strong positive correlate with the average number of osmiophilic granules (P＜0.05), weak positive correlate with the average numbers of starch granules, the length of chloroplast and the density of stomas(P＞0.05). Furthermore δ13C was weak negative correlated with the length of starch grain and the density of glandular hairs (P＞0.05). The results indicated that (1) stable carbon isotope composition was varied in different tobacco cultivars and (2) the variation was associated with leaf ultrastructure