The article deals with social instrumental intention of rumours and their expression. It also reveals the social and political role of rumours in controlling the behaviour of a group of members and preserving its identity. The dual nature of rumours is analyzed as well as gnosiological, psychological and sociological reasons. On the one hand, the roots of rumour vitality are hidden in the dualism of this phenomenon, where in a strange way contradictory things get on well together ­ private and public, moral and immoral, the truth and the lie, between which it is not easy to draw a clear boundary even in everyday life. On the other hand, a rumour is alive because of our constant thirst for additional and fresher information, trying to perceive a person, an action or a phenomenon better. At the same time, it stimulates the proclaimers of the official political information to find the ways for the provided information to be more accurate, open, exhaustive as possible, presented in an understandable and accessible form. There the power of the effect of a rumour lays, a phenomenon without authorship, but with an authority to which, more or less, all of us are to obey.