Nitrosylsulfuric acid is the chemical compound with the formula . It is a colourless solid that is used industrially in the production of caprolactam, and was formerly part of the lead chamber process for producing sulfuric acid. The compound is the mixed anhydride of sulfuric acid and nitrous acid.
In organic chemistry, it is used as a reagent for nitrosating, as a diazotizing agent, and as an oxidizing agent.