Nitrous acid behaves as reducing as well as an oxidising agent. It reduces potassium permanganate, potassium dichromate, ${\mathrm{H}}_2{\mathrm{O}}_2$ and other strong oxidising agents. It oxidises strong reducing agents such as hydroiodic acid, sulphurous acid etc.

It oxidises $\mathrm{F}{\mathrm{e}}^{+2}$ into $\mathrm{F}{\mathrm{e}}^{+3}$ in acidic medium;

$\mathrm{F}{\mathrm{e}}^{+2}+\mathrm{H}\mathrm{N}{\mathrm{O}}_2+{\mathrm{H}}^{+}\to \mathrm{F}{\mathrm{e}}^{+3}+\mathrm{N}\mathrm{O}+{\mathrm{H}}_2\mathrm{O}$

It reduces acidified $\mathrm{K}\mathrm{M}\mathrm{n}{\mathrm{O}}_4$ .

$2\mathrm{K}\mathrm{M}\mathrm{n}{\mathrm{O}}_4+3{\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4+5\mathrm{H}\mathrm{N}{\mathrm{O}}_2\hspace{0.33em}\to$

${\mathrm{K}}_2\mathrm{S}{\mathrm{O}}_4+2\mathrm{M}\mathrm{n}\mathrm{S}{\mathrm{O}}_4+3{\mathrm{H}}_2\mathrm{O}+5\mathrm{H}\mathrm{N}{\mathrm{O}}_3$