A high-voltage disconnection knife insulated by air for external use in high-voltage electrical transmission and distribution networks, the disconnection knife includes two copper arms for the disconnection or contact, mounted in a parallel relation to each other, a front and rear contact base, a turning support in the vicinity of the rear base such that the arms turn at one of its ends about an axis perpendicular to them, a central copper block for distribution of the current flowing through the copper arms; the distance between the arms is defined by the set of stainless steel axes, the copper block and the turning mechanism. At the ends of the disconnection arms an aluminum spring of with transverse section of gradually reduced thickness is connected to the external surface, said spring being fixed to the ends of the arms by means of a pair of stainless steel axes. The front and rear L-shaped bases are formed by the bending of a copper sill with rounded edges to define an area of contact.