Rhodamine B is a greenish powder dye which is water soluble and is often used as a tracer dye to determine the rate and direction of flow and transport. Its chemical formula is C28H31ClN2O3 and molecular weight is 479.01 kDa. Its lambda max is 542-554 nm and melting point is 210-211 C. _. It has role as a fluorochrome, a fluorescent probe and as a histological dye. It is an organic chloride salt and a xanthene dye. Rhodamine dyes fluoresce and can thus be detected easily and inexpensively with fluorometers. Rhodamine dyes are used extensively in applications such as fluorescence microscopy, flow cytometry, fluorescence correlation spectroscopy and ELISA.

It can also be used as a dye especially for paper, as a metal chelating reagent, and in drugs and cosmetics. It can be stored at room temperature.