Nitrosylation is a protein modification, in which a nitrosyl group is post-translationally added to a protein.

There are a range of enzymes that produce nitric oxide, and the frequent consequence of this production is nitrosylation.

S-nitrosylation is a biologically important reaction of nitric oxide; it refers to the conversion of thiol groups, including cysteine residues in proteins, to form S-nitrosothiols (RSNOs). S-Nitrosylation is a mechanism for dynamic, post-translational regulation of most or all major classes of protein.