To assess the short- and long-term impacts of UV radiation (UVR, 280-400 nm) on the microalga Scrippsiella trochoidea, we exposed cells to three different radiation treatments (PAB: 280-700 nm, PA: 320-700 nm, and P: 400-700 nm). A significant decrease in the photochemical efficiency (ΦPSII) at high irradiance (100% of incident solar radiation, 216.0 W m-2) was observed. Photoinhibition was reduced from 62.7 to 10.9% when the cells were placed in 12% solar radiation (26.1 W m-2). In long-term experiments (11 days) using batch cultures, cell densities during the first 5 days were decreased under treaments P, PA, and PAB, reflecting a change in the irradiance experienced in the laboratory to that of incident solar irradiance. Thereafter, specific growth rates increased and UV-induced photoinhibition decreased, indicating acclimation to solar UV. Cells were found to exhibit both higher ratios of repair to UV-related damage, shorter period for recovery and increased concentrations of UV-absorbing compounds (UVabc), whose maximum absorption was found to be at 336 nm. Our data indicate that S. trochoidea is sensitive to ultraviolet radiation, but was able to acclimate relatively rapidly (ca. 6 days) by synthesizing UVabc and by increasing the rates of repair processes of D1 protein in PSII. and W. C. Guan, S. H. Lu.