Fuchsine (sometimes spelled fuchsin) or rosaniline hydrochloride is a magenta dye with chemical formula C₂₀H₁₉N₃·HCl. There are other similar chemical formulations of products sold as fuchsine, and several dozen other synonyms of this molecule.

It becomes magenta when dissolved in water; as a solid, it forms dark green crystals. As well as dying textiles, fuchsine is used to stain bacteria and sometimes as a disinfectant. In the literature of biological stains the name of this dye is frequently misspelled, with omission of the terminal -e, which indicates an amine. American and English dictionaries (Webster's, Oxford, Chambers, etc.) give the correct spelling, which is also used in the literature of industrial dyeing. It is well established that production of fuchsine results in development of bladder cancers by production workers. Production of magenta is listed as a circumstance known to result in cancer.