A joining device (8) for hybrid wind turbine towers (5) intended for the fixation of a metal portion (6) of a wind turbine tower (5) to a concrete portion (7) of said wind turbine (1) which comprises a metal body (9) having a generally tubular configuration that is suitable to be fixed to the metal portion (6) of the tower (5) which in use is adjacent to the concrete portion (7), and suitable for being at least partially embedded into said concrete portion (7), said metal body (9) being provided with a number of anchoring openings (11) adapted such that the material of the concrete portion (7) passes therethrough. A hybrid wind turbine tower (5) comprises such a joining device (8) provided between one metal portion (6) and one concrete portion (7).