Herein, we report the use of ultraviolet (UV) irradiation as a method for inactivating allergen proteins to enhance the effect. In our experiments, we used eight kinds of UV light at various wavelengths, which were produced with four different light sources and two different band-pass filters. To determine the resulting degree of effect, we calculated the concentration change ratios of antigen-antibody reactions for solutions containing the purified antigen of Japanese cedar pollen allergen (Cry j 1) before and after UV irradiation. From these results, short-wavelength UV light had greater inactivation effects on Cry j 1 compared to long-wavelength UV light in the range from 240 to 220nm. Wavelength dependence is a possible explanation that the absorbance of allergen protein increases as the wavelength decreases, because the absorbance characteristics of ordinary protein are similar to the effect changes.