Different diameter CdSe/ZnS semiconductor nanocrystals (average diameter: from approximately 3.5 to approximately 20 nm), quantum dots (QDs) were synthesized by changing the nucleation time, using organometallic reagents. These quantum dots possess narrow and symmetrical fluorescent emissions. The emission wavelengths of these composite dots span most of the visible spectrum from 500 through 700 nm. Furthermore, it is found that the quantum dots with an emission at approximately 590 nm, tend to have a good quantum yield (such as Phi(590)=43.5%). While the emission wavelength of prepared CdSe/ZnS QDs shifts toward blue or red from 590 nm, the quantum yield tends to decrease. After that, optical encoding of microbeads with these quantum dots was carried out, and the spectra of encoded beads were identified. The result indicates that, to identify the encoded beads with different emission wavelengths and emission intensities, it is needed to acquire and differentiate the spectra of beads. After immobilized with human IgG, the encoded beads were used to detect the corresponding antibody in solution. The result indicates that the encoded beads can detect the antibody signal effectively. And the effective detection range of the antibody is about 2-15 microM.