Tetraiodo phenol sulfonphthalein (TIPSP) reacts with protein rapidly to form the dye-protein complex with an absorbance maximum at 617 nm. Water is used as the blank instead of the reagent blank because the reagents have no absorption at this wavelength; thus the operating steps are simplified. Under the experimental conditions (0.03 mM TIPSP, pH 2.63), the linear range of this assay is composed of three parts: 10.2–54.4μg·ml−1, 54.4–95.2 μg·ml−1and 95.2–136.0 μg·ml−1. Most amino acids, reducing reagents (e.g. ascorbic acid) and complexing reagents (e.g. EDTA) don't interfere with the assay. The interferences from detergents, salts and ethanol can be minimized by dilution. In detection of human serum albumin, this method gave results close to that of the bromocresol green assay.