Abstract: New (bo) values were measured for 64 K - white mica specimens from the Menderes Massif (W. Turkey) by XRD. The mean value for (bo) parameters was found to be 9028 °A. The pressure of metamorphism of theMenderes Massif lies in the range between low and high pressures, that is intermediate. During the Alpine metamorphism, two metamorphic phases of different pressure developed in edge central regions of the Massif. The (bo) parameter of muscovite in the K. Menderes group is higher than of the other two groups (Ören and Milas) and Ören groupis smaller than that of the other two. It is determined that the (bo) values K. Menderes group mean value 9.036, Milas group mean value 9.035 and Ören group mean value 9013 (represent the results of the younger phase in theedge terrain of the Massif). The cummulative frequency curves of parameter (bo) of Menderes Massif is compared tomassives all over the world.