Within the Aegean extensional system, the izmir-Balikesir Transfer Zone (IBTZ) is a crucial element in the late Cenozoic evolution of western Anatolia since it accommodates the differential deformation between the Cycladic and the Menderes metamorphic core complexes. Here, we determine the rotational history of western Anatolia using new paleomagnetic data from 87 sites in Miocene volcano-sedimentary rocks to better understand the role of the IBTZ. Our results reveal two discrete and opposite major rotational phases during the Miocene. The first phase is derived from early Miocene volcanic, sedimentary and granitic rocks and is controlled by detachment and strike-slip faults. It is characterized by an average (net) 23 +/- 6 degrees clockwise (CW) rotation within the Diaz since the early Miocene. Our new data from the Menderes part on the other hand show an average -23 +/- 10 degrees counter-clockwise (CCW) rotation. The data from the Cycladic part show no significant (net) rotation since the early Miocene. The second phase is derived from middle-late Miocene volcanic and sedimentary rocks and is controlled by high-angle normal and strike-slip faults. The rotations from this phase show a very consistent pattern of -22 +/- 11 degrees CCW within the IBTZ, while now the Menderes part shows an average CW rotation of 25 +/- 14 degrees.