Th e toxigenic cyanobacterium Cylindrospermopsis raciborskii previously restricted to tropical latitudes, has been increasingly reported in temperate lakes in recent decades. Th e causes of its biogeographical expansion are under investigation, but effi cient physiological adaptation to changes in temperature and light regimes are likely to be involved. Th e present study evaluated the morpho-physiological responses of a strain of C. raciborskii from southern Brazil to nine light intensities, from 9 to 250 μmol photons m -2 s -1 . Blooms of this cyanobacterium are regularly recorded in the region. Morpho-physiological responses were measured based on growth rate and trichome length. Cylindrospermopsis raciborskii showed slow growth at low light intensities, 9 and 20 μmol photons m -2 s -1, and responded morphologically by increasing the length of trichomes. In turn, the strain displayed constant maximum growth rates at light intensities higher than 50 μmol photons m -2 s -1. Th ese results support the hypothesis that C. raciborskii can survive under low light conditions and continue to produce viable trichomes. Moreover, the strain achieved high growth rates under a relatively wide range of light intensities, a physiological adaptation that can potentially be a competitive advantage in the phytoplankton community.