This study was conducted to obtain the breeding Information for varietal difference of leaf breakdown of flue-cured tobacco at Taegu Experiment Station, Korea Ginseng & Tobacco Research Institute In 1988. The experiment was designed in randomized block with 3 replications. And data were analyzed as spilt plot design composed with varieties for main and growth stages for sub-plots. Among the 8 varieties (NC 95, SL 72, Sleight G-28, TC 518, NC82, NC 2326, NC 567 and TC 499), first half derived from NC 95, and 4 latter varieties were used for check Plants and not derived from NC 95. Plant seedlings were transplanted in 15 April. The number of breakdown leaf were investigated twice at peak growth stage, 5 June and at early harvest stage, 30 June. NC 95 and varieties derived from NC 95 had showed significantly different on the number of breakdown leaf compared to the latter 4 ones after heavy rainfall, but there were not significantly different at the two growth stages. It was suggested that NC95 and varieties derived from NC 95 had substance to induce leaf breakdown by conditional genes after water absorption to plant tissue. Among the varieties derived from NC 95 cultivar SC 72, Speight G-28 and TC 518 had appeared significantly different on the number of breakdown leaf, respectively. These results could appreciated analogically that character of leaf breakdown were governed by heteromeric genes In NC 95.