A fairing for a modular blade of a wind turbine generator, comprising including a joining zone disposed between two consecutive modules of the modular blade. The fairing is comprised of different components; the suction side fairing, the pressure side fairing and auxiliary components, such as tabs to facilitate the joining of the components. The leading edge fairing and the trailing edge fairing are constituted of an elastomeric material, preferably silicone, supported in a rigid glass fibre framework in order to absorb the warping experienced by the blade during the operation thereof. The attachment elements employed to join the fairings together and to the setbacks of the blade shell are rivets or similar. All the fairings incorporate the metal elements necessary to be equipotentially bonded, being linked to the lighting down-drop.