Basic dye, also known as basic group dyes, is the salt generated by aromatic bases reacting with acids (organic and inorganic acids), videlicet that is colored organic base salts whose basic group is generally amino, which becomes -NH2 • HCl salt groups when the salt occurs. The groups dissolve in water, dissociated into dye cations and acid anions. Thus the dye is also known as cationic dyes.

In 1856 H.W.perkin synthesized mauveine guilty basic dye, the first synthetic dye in the world. Following then it gradually emerged types of Basic Fuchsin (CI Basic Violet 14), basic blue (CI Basic Blue 9), crystal violet (CI Basic Violet 3), malachite green (CI Basic Green 4) and Rhodamine (CI basic violet 10). The chemical structure of basic dyes includes aromatic methane, triarylmethane, azo type and nitrogen-containing heterocyclic compounds (such as xanthene, oxazine and thiazine, etc.).

There are less hydrophilic groups in basic dyes so that they are insoluble in water. When we dissolve them, we use alcohol or acetic acid and then dilute with water. Basic dyes are sensitive to temperature, so that both temperature of the dissolution-dilution and dye-bath should not be too high. Basic dyes have affinity with leather surface with a negative charge so it is suitable to dye vegetable tanned leather. Mainly used for leather belt anions (vegetable tanned leather) for dyeing, its binding force is strong. It is also used for chrome tanned leather with cationic because it owns light permanency and is seldom used.

Basic dyes are organic alkali salts and when in solution, they dissociate into cations and anions pigment, so they are also known as basic group dyes. The molecular structure generally contains primary amines, secondary amines, tertiary amines or nitrogen-containing heterocyclic ring, leading to the weakly cationic in acid bath.

Basic dye tints strongly with bright shade. But the light permanency and endurance washing natures of such dyes are poor. Thus it is now rarely used for coloring fibers and mainly used for coloring paper, ribbon and biological materials and so on. Crystal Violet, rhodamine and oxazine dyes are also used as thermal dyes, sensitive dyes and dye lasers.