To study the effect of nitric oxide on longevity and some qualitative characteristics of cut carnation flowers (Dianthus caryophyllus cv. Nelson), cut flowers were treated for 48 hours with Sodium Nitroprusside (SNP) as a source of NO° donor at four concentrations (0, 20, 50 and 100µM) alone and in combination with other such ethylene inhibitors as thidiazuron and sucrose in a completely randomized design with three replication where the temperature was 20?2?C, 60–70% relative humidity,
15-20?mol s-1m-2 light intensity and 12 hours of photoperiodism. The flowers were then transferred into distilled water. The vase life of cut flowers, their appearance, chlorophyll content, stem firmness, and water absorption rate were recorded. The results indicated that the concentration treatments of 50 and 100µM SNP resulted in increase in vase life in comparison with control; also concentration treatment of 50µM thidiazuron maintained the chlorophyll in leaves in contrast to control when on the 8th day after treatment. The treatment of 50µM thidiazuron resulted in the best quality of appearance, and the treatment of 50µM thidiazuron as well as that with 30mM sucrose resulted in high water absorption in comparison with control. Concentration treatment of 100µM Sodium Nitroprusside alone and treatment with 100µM SNP in combination with 50µM of thidiazuron on were effective stem firmness.