Abstract: In order to investigate the response of microalgae to UV-B radiation and their physiological mechanism, and to improve their potential value, we selected Asterarcys sp. SCSIO-44020 as material, and exposed them to UV-B radiation under different radiation conditions (0, 10, 30, 50 and 70 min each time, corresponding to radiation doses of 0, 150, 460, 770 and 1 050 mJ·cm⁻²) every 48 h until the end of the culture. The results show that, after a 20-day cultivation, UV-B radiation of 10–50 min treatment group had no significant effect on the growth of algae compared with the control group (P>0.05), but the 70 min treatment group inhibited the growth significantly (P<0.05). With the increase of UV-B radiation time, the protein content increased gradually, but the total lipid content decreased, with no siginificant differences between different groups and the control group (P>0.05). The total carotenoid and mycosporine-like amino acids (MAAs) contents increased with the increase of UV-B treatment time, and reached the maximum values in 70 min treatment group, 1.75 times that of the control group. However, compared with the control group, the total carbohydrates and MAAs yields in 50 min treatment group increased 12.40% and 57.61%, respectively, reaching the maximum values. In conclusion, Asterarcys sp. has a strong ability to resist UV-B radiation, and the increase of MAAs is the key to its adapting to UV radiation. Moreover, intermittent treatment of 50 min UV-B radiation is an effective approach to regulate the production of MAAs and other products in microalga.