This paper reviews some of the results described in the literature on the effect of UV-B radiation on ciliated protozoa, concentrating in particular on the changes induced in motility and photomotility, which are both important in determining the capability of these organisms to survive in their environment. It will be shortly described what ciliates are and why they are an important component of ecological systems. A summary will follow of the early works, where the effects of UV radiation on ciliates were investigated. Finally, it will be described in some more detail the results of studies on a marine ciliate, Fabrea salina, and two fresh-water ciliates, Blepharisma japonicum and Ophryoglena flava.