Abstract: The exposed core gneisses of the Menderes Massif had been sampled form three regions (form South toNorth, Çine ,and Ödemiş Massifs, Gördes Massif ,and Eğrigöz Massif). These samples had been investigated by the X-Ray,electronmicroprobe ,and microscopic methods .The cell parameters of K-feldspars ,and their bo, txm, tso, t2m values (thescattering1 probability of Al atoms in the four kinds of tetrahedrons) had been calculated from more than 50 samples bythe X-Ray Method. Chemical composition of K-fieldspars ,and their perthitic albite flakes ,and also coexistent plagioslaseswith K-feldspars had been determined by electronmicroprobe.From the point of structural view the calculated unit cell parameters, with small regional variations .display theK-feldspars to be in intermediate microcline state. Beside that, the K-feldsp,ars, derived as microcline f rom X-Ray filmsmust have been framed by very tiny triclinic domains .which could hardly be recognized by X-ray procedures. Also thetjO, tjin, tso ,and t2m values indicate that the studied crystalls are in intermediate microcline state.The An percent of coexistent plagioclases with K-feldspars shows a variation from 8 to 25. This variation is dueto Ca occurences of different values within the derived metamorphic rocks from sedimentary rocks. Over 17 >% Anvalues of plagioclase ,and observed poligonization texture of feldspar ,and quartz indicate that these rocks fiormed abovethe medium grade metamorphic phase (^,540°C).The results can be outlined under the scope of the petrogenetic evolution of Menderes Massif as follows: MonoclinicK-feldspar occurences in primary sedimentary units which had later .become Augen Gneisses of Menderes Massif, firsttransformed to triclinic forms by the rising temperature ,and then retransformed to monoclinic forms at the oligoclaseformation boundary (550°C).Occurence of sillimanite in the whole series from South to North indicates that the metamorphism reached to thebeginning temperatures of migmatization (680°C). But, triclinic metric, whick is a general retriclinization product inK-feldspar occurences in Augen Gneiss, conforms that the formation temperature is around 450° C. This evidence indicates that young alpidic phases made only retrograde metamorphic effects on Menderes Massif. The 66+4 milion yearsradiometric age of muscovites from Augen Gneisses near Çine shows an agreement with the age of the young alpidicphase. As a result, main metamorphic phases which caused to progressive metamorphism in Menderes Massif are olderthan that alpidic phase.