The vase life of cut flowers, or flower longevity, is one of the most important characteristics that determine their quality and their ability to satisfy consumer preferences. To improve the vase life of carnations, conventional cross-breeding techniques were used to develop many carnation lines with a long vase life. Two new cultivars, ‘Miracle Rouge’ and ‘Miracle Symphony’, with a genetically determined long vase life, were developed. They had vase lives of 17.7 to 20.7 days (3.2 to 3.6 times the vase length of the ‘White Sim’ cultivar) under standard conditions (23°C, 12-h photoperiod, 70% RH). The ethylene biosynthesis pathway in these cultivars was almost completely blocked during natural senescence, which was responsible for the long vase life. Changes in ethylene sensitivity with flower senescence were evaluated using a time-lapse video recording system, which provides a simple and accurate way of evaluating ethylene sensitivity. The video system revealed that the ethylene sensitivity of various cultivars including ‘Miracle Rouge’ and ‘Miracle Symphony’ after anthesis decreased with increasing age.