The flowering decreases the yield and quality of material tobacco. Tobacco plants have normally response with short-day photoperiodism. So that, the long-day photoperiodism or interruption of the dark period by one hour of the light are capable to inhibite the flowering of the shor-day plants. Study was carried out at tobacco variety K326 cultivated popularly in Vietnam. The results showed that the photointerruption of the night by red or white light as well as addition of 2, 4, 6 hours/day (long-day photoperiodism equal 14 h light/10 h dark, 16 h light/8 h dark and 18h light/6 h dark) promoted the stem and leaf growth and inhibited significally the flowering of tobacco. The light treatment of both long-day photoperodism (plus 4 and 6 h/day) or photointerruption in the night by the red or white light at the variant continous to the flowering were able to retardance the flowering time upto 28-34 days.