A novel fluorescence detection system using a chemosensor for phosphoprotein in gel electrophoretic analysis has been developed. The system employed the alizarin red S-aluminum (III)-appended complex as a fluorescent staining dye to perform the convenient and selective detection of phosphorylated proteins and total proteins in SDS-PAGE, respectively. Therefore, a full and selective map of proteins can be achieved in the same process without resorting to other compatible detection methods. As low as 62.5 ng of alpha- (seven or eight phosphates) and beta-casein (five phosphates), 125 ng of ovalbumin (two phosphates), and kappa-casein (one phosphate) can be detected in approximately 135 min, with the linear responses of rigorous quantitation of changes over a 1254000 ng range. As a result, alizarin red S-aluminum (III) stain may provide a new choice for selective, economic, and convenient visualization of phosphoproteins.