A foundation for a wind turbine tower, provided with a central accommodation for accommodating and firmly constraining, by means of threaded bars projecting from such central accommodation, an actual wind turbine tower, made of steel or concrete, is entirely prefabricated and includes at least two prefabricated structural elements, modular and monolithic, made of reinforced concrete, approached in sequence, shape-coupled, and subsequently constrained to each other, at least at such central accommodation, by a series of post-tension cables arranged in respective through-holes, so as to make the entire foundation monolithic.