PUA composite particles were prepared by seeded surfactant-free emulsion polymerization, the polyurethane (PU) aqueous dispersions were used as seed particles. The studies on the UV spectra of PUA composite emulsions were carried out, the results showed that the maximum absorbance of n-pi* transition evidently shifted to red wavelength with increasing the concentration of the aqueous PU seed dispersions; the UV absorbance of PU dispersions decreased with increasing the amounts of the hydrophilic chain-extender and increased with increasing the NCO/OH molar ratios; when the hydrophilic chain-extender was 7.5%, the UV absorbance of PUA composite emulsion reached the lowest, the type of initiators showed less influence on the absorbance of UV spectra of PUA composite emulsions. Moreover, the UV spectra of PU dispersions and the diameters of PUA composite emulsion particles were nearly correlative.