Abstract: Nitric oxide (NO) is one of the most important signalling molecules of plant. It is involved in many processes of plant development, such as seed germination, hypocotyl elongation, leaf expansion, root growth, lateral roots initialation, apoptosis, and resistance to adverse environments. A great deal of evidence suggested that plant can produce NO by enzymes similar to the nitric oxide synthases in mammalian. In addition, plant can also produce NO by nitrate reducta se. Although the signalling pathways through which NO functioned in plants are still vague at present, plant might adopte the similar mechenisms of NO signalling in animals. Since most processes of plant development are regulated by plant hormones, more and more attentions have been drawn to reveal the relationships between NO and plant hormones. Regulating hormones banlance seems to be a possible mode of action of endogenous NO in plants.