Nitrosylsulfuric acid is the chemical compound with the formula HSO4NO.

It is a colourless solid that is used industrially in the production of caprolactam,[3] and was formerly part of the lead chamber process for producing sulfuric acid.

[1] A typical procedure entails dissolving sodium nitrite in cold sulfuric acid:[4][5] It can also be prepared by the reaction of nitric acid and sulfur dioxide.

[6] HSO4NO is used in organic chemistry to prepare diazonium salts from amines, for example in the Sandmeyer reaction.

Related NO-delivery reagents include nitrosonium tetrafluoroborate [NO]+[BF4]− and nitrosyl chloride.