The aim of this research was to analyse the strategies of study used by the participants to an on line course at University, managed with a Knowledge Building approach. Eight students of the 4th year of Psychology at University of Padua (Italy) took part in this research. The activity was developed in some on line discussion, supported by Knowledge Forum, about different themes. The data have been analysed using an ethnographic method, with the software ATLAS-ti. The results show that the students underline three main questions about the strategies experimented: a more active elaboration of content, the cooperative interaction as a strategy of inquiry, a bigger metacognive control of the own comprehension.