A method for protein determination using eosin Y is described. Eosin Y reacts with proteins under acidic conditions and forms an intense pink proteineosin Y complex with an absorbance maximum of 535-545nm. The color produced from this reaction is stable and its absorbance increases proportionally over a wide range of protein concentrations (standard assay, 50-1000μg/ml of BSA; microassay, 1.25-50μg/ml of BSA). The eosin Y method can be performed at room temperature without further incubation after vortex mixing. The assay has advantages such as (i) simple procedures, (ii) stable dye-protein color with no precipitation of dye-protein complex for at least 72h, (iii) good reproducibility and (iv) rapid reaction. The characterization of the eosin Y method extends its best application to a routine protein determination in solution.