Within the framework of a large campaign of coordinated multifrequency observations of the T-Tauri Star RU Lupi, we present simultaneous UV, optical and IR energy distributions secured in the years 1984-86. The observations have been carried out with lUE satellite and ESO optical and IR telescopes. Strong variations on different time-scales have been detected in UV and optical regions. On June 30, 1986 a large flare was observed. An analysis of the different energy distributions indicates that the variability of RU Lupi is mainly due to a strong activity in the surface layers of the star.