In vitro tests with Hippeastrum, the bulbs of 3-year-old plants and with 20-22 cm circumference were cut into sixteen parts evenly (1/16) for scaling study. A significant decrease in contamination rate was observed by pasteurizing the bulbs at 50℃ hot-water for 90 minutes or 55℃ for 45 minutes. The greast bulblet number was fond in the sugar 50 g/l hot-treatment. In comparisons of sucrose sources, the largest number of bulblet formation was obtained in glucose : fructose = 15 g/l : 15 g/l treatment and the smallest was found in fructose 30 g/l only. It was revealed that Bulblet formation was promoted while activated carbon was added on the medium under the light conditions and the bulbs from treated plants was often heavier than the control set. BA supplement enhanced bulblet formation, however, bulblet growth and development was not promoted. Therefore, the BA concentration is better to remain below 2.0 mg/l when twin-scaling in vitro.