Modular autonomous mobile fence, delimiter of grazing areas. It consists of two structures (10, 20) arranged opposite and distant from each other. Each structure (10, 20) is composed of at least two movable towers, arranged at the ends of the very same row and structurally linked to each other to form a movable row. An electric wire conductor (14, 15) is arranged between these two rows (10, 20) and forms a closed quadrilateral that delimits a closed grazing area (16). Said rows with towers and the area delimited by the electric fence can be selectively moved from one lot to the next, together with the animals kept therein. Said electric fence must have means of separation (31, 32) of the electric conductor from the ground (14, 15) and at least one of the mentioned towers must have means of tensioning (34) the electric conductor.