In chemistry, the amino radical, ·NH₂, also known as the aminyl or azanyl, is the neutral form of the amide ion (NH−2). Aminyl radicals are highly reactive and consequently short-lived, like most radicals; however, they form an important part of nitrogen chemistry. In sufficiently high concentration, amino radicals dimerise to form hydrazine. While NH₂ as a functional group is common in nature, forming a part of many compounds (e.g. the phenethylamines), the radical cannot be isolated in its free form.

Amino radicals can be produced by reacting OH radical with ammonia in irradiated aqueous solutions. This reaction is formulated as a hydrogen abstraction reaction.

The rate constant (k₁) for this reaction was determined to be 1.0×10⁸ M⁻¹ s⁻¹, while the parallel reaction of OH with NH⁺
₄ was found to be much slower. This rate was redetermined by using two-pulse radiolysis competition methods with benzoate and thiocyanate ions at pH 11.4. A value of k₁ = (9 + 1)×10⁷ M⁻¹ s⁻¹ was obtained from both systems. While in acidic solution, the corresponding reaction of ·OH with NH+4 is too slow to be observed by pulse radiolysis.

The amino radical may also be produced by reaction of e⁻(aq) with hydroxylamine (NH₂OH). Several studies also utilized the redox system of Ti^III−NH₂OH for the production of amino radicals using electron paramagnetic resonance (ESR) spectroscopy and polarography.

Reduction of hydroxylamine by e⁻(aq) has also been suggested to produce the amino radical in the following reaction.

The reactivity of the amino radical in this reaction is expected to be pH dependent and should occur in the region of pH 3–7.

The amino radical has two characteristic electronic states:

The more stable electronic state is ²B₁, where the unpaired electron is in the p-orbital perpendicular to the plane of the molecule (π type radical). The high energy electronic state, ²A₁, has the two electrons in the p-orbital and the unpaired electron in the sp² orbital (σ type radical).