Abstract: Nostoc flagelliforme Bornet & Flahault, named popularly as 'Facai' in Chinese, is a terrestrial cyanobacterium of great economic value. Although aquatic-living colonies were developed under indoor conditions, little is known whether they could and how they would adapt to solar radiation. Therefore, we exposed the colonies to different solar radiation treat-ments, photosynthetically active radiation (P:PAR,395-700 nm), PAR+ultraviolet radiation-A (PA,320-700 nm) or PAR+total ultraviolet radiation (PAB,280-700 nm). Changes of their growth, effective quantum efficiency (△F/F'm) and pigments were estimated during the experimental period. It was found that high levels of both PAR and ultraviolet radiation (UVR,280-395 nm) reduced the △F/F'm of the colonies. △F/F'm was reduced about 54% by PAR and further declined 13% by UVR. The △F/F'm recovered in the late afternoon. After two days' acclimation to solar radiation, the biomass of the colonies increased during the following days. UV-absorbing compounds, scytonemin and mycosporine-like amino acids (MAAs), increased by 124 and 9 times, respec-tively, in 9 days. Such increased UV-absorbing substances played an important role in protecting the aquatic-living colo-nies of Nostoc flagelliforme from solar UVR. The results may be useful for the mass production of the aquatic-living colo-nies of Nostoc flagelliforme under outdoor conditions.