Abstract：The mechanism of color changes between Fuchsine Acid (FA) and Bovine Serum Albumin (BSA) was studied by spectra probe. And the influence of different experimental conditions on the absorption spectra of FA-BSA mixtures was investigated. Through these experiments, one would draw the conclusion that the color changes of FA-BSA complex results mainly from the hydrophobic interaction between FA and BSA while the electrostatic interaction is still necessary for the formation of pink FA-BSA complex.