Enhanced UV-B radiation resulting from ozone depletion in stratosphere with the increase of human activities can harm plants greatly, whereas the change of nitrogen supply can affect the sensitivity and resistance to UV-B radiation in plants. Foxtail millet (Setaria italica (L.) Beauv.), a typical C₄ crop plant, was chosen as experimental model to investigate the effects of enhanced UV-B radiation and nitrogen supply on photosynthetic pigments and non-enzymatic protection system in leaves. The plants of foxtail millet were fertilized under two different nitrate-nitrogen conditions (1.875, 15 mmol/L) from the jointing stage to the grouting stage, and were stressed by two different intensities of enhanced UV-B radiation (4.29, 7.12 kJ·m^-2·d ^-1) from the heading stage to the grouting stage (26 days). During this period, the photosynthetic pigments and flavonoids content and the phenylalanine ammonia-lyase (PAL) activity in leaves of foxtail millet were measured. The nitrogen supply showed significant effect on the photosynthetic pigments contents in leaves of both UV-B treated and non-treated foxtail millet. The leaves in low nitrogen supply group showed significantly lower photosynthetic pigments content but higher carotenoid/chlorophyll ratio when compared to those of high nitrogen supply group according to most of statistical test results (P<0.05, least-significant difference, LSD). However, enhanced UV-B radiation treatment showed significant effects on the photosynthetic pigments contents in leaves of foxtail millet in only the 11th day and the 21st day, and the photosynthetic pigments were more sensitive to enhanced UV-B radiation treatment at the high nitrogen group compared to the low nitrogen group. The nitrogen supply showed significant effect on PAL activity in leaves of foxtail millet during the whole period of this experiment, whereas enhanced UV-B radiation showed significant effect on the PAL activity only after the 11th day. Meanwhile, most LSD results showed that the PAL activity in leaves of foxtail millet increased in the low nitrogen supply group compared to the high nitrogen group, whether treated by enhanced UV-B radiation or not. Furthermore, both the nitrogen supply and enhanced UV-B radiation affected the flavonoids content in leaves of foxtail millet significantly after the 16th day, and the flavonoids content in leaves increased significantly in the low nitrogen supply in the 26th day independent of enhanced UV-B radiation. There was a significant positive correlation between the flavonoids content and the PAL activity, but both the flavonoids content and the PAL activity had a significantly negative correlation with the chlorophyll content. Moreover, there was a significant correlation between the chlorophyll content and the carotenoid content. This study indicated that in leaves of foxtail millet, low nitrogen supply treatment could enhanced accumulation of flavonoids and the carotenoid/chlorophyll ratio, thus caused more stability of photosynthetic pigments contents when foxtail millet was stressed by enhanced UV-B radiation compared to the high nitrogen supply during the breeding period. Therefore, low nitrogen supply treatment may improve the resistance to UV-B radiation in plants.