Varietal response to cool temperature(18$^{circ}C$) and short (8hr.)-day treatment were investigated under controlled conditions of Phytotron in the Suwon Agronomy Experiment Station. Five flue-cured and one burley tobacco varieties (Nicotiana tabacum L.) were used, and the length of treatment ranging from 8 to 32 days at 3-day intervals and also includes continuous treatment up to the plants were flowered. The days to flower decreased significantly than the no treatment when the length of treatment was 11 to 14 days for the varieties NC82, Br.21 and NC22NF, and 17 to 26 days for SPG-28, Mc.944 and TC499, respectively. And also the number of leaves decreased significantly than the no treatment when the length of treatment was 8 days for NC22NF, 11days for NC82 and Br.21, 14 days for Mc.944, and 17 days for SPG-28 and TC499, respectively. The maximum decreasing ratio of the leaf number by the cool temperature and short-day treatment were 47.7 to 58.5% for NC82, Br.21 and NC22NF, and 38.9% for Mc.944, 33.4% for SPG-28 and 29.0% for TC499, respectively.