Quantum dots (QDs) as a biological labeling material for medical applications need to be evaluated for the sensitivity and stability of their fluorescence. Comparison of QD-based immunolabeling and commonly used immunohistochemical staining in detecting the expression of prostate stem cell antigen (PSCA) in bladder tumor tissues revealed that the two methods had similar sensitivity in the differential display of PSCA expression correlated with tumor stage and grade (kappa=0.92, p<0.001). In addition, the intensity of QD fluorescence remained stable for at least 10 days after conjugation to the PSCA protein and nearly 96% of the positive expression in samples lasted for one month.