Nitric oxide (NO) is a relatively short-lived inorganic free radical, which can be produced by different types of cells in multi-cellular organisms. This diffusible messenger functions as either an effector or a second messenger in many intercellular communications or intracellular signaling pathways. NO becomes noxious if it is produced in excess. These effects are mainly mediated by the reactivity of NO with various reactive oxygen species, which can be countered by antioxidant enzymes. In addition, NO can directly modify biological molecules via S-nitrosylation and lead to altered signaling responses. Accumulating evidence suggests that NO has a double-edged role in a dose-dependent, cell-type specific, and biological milieu-dependent way. In the present review, we summarized the synthesis and signaling pathway of NO, and especially focused on its involvement in biological processes, such as endoplasmic reticulum stress, apoptosis and autophagy. Besides, we discussed the functions of NO in the nervous system and its potential role in neurodegenerative diseases. We proposed the target on NO may shed light on the treatment of the related diseases.