A lid of a container, particularly beverage container, comprising an opening for emptying the container, fitted with guides formed on two opposite walls and with a slide piece for opening and reclosing the said opening, where there are two catches formed on the top surface of the slide piece, the catches fitted slidingly in the opening on the said guides, and where the slide piece is fitted with technical means for shifting the slide piece from the closed position to the open position and backwards, is characterised in that the surfaces (2a) of the catches (2) of the slide piece (1) which cooperate with the guides (4) are inclined at an acute angle (α) with respect to the top surface of the slide piece (1) positioned under the said surfaces (2a) of the catches (2).