Seventy samples from major plutons (mainly granitic) of Western Anatolia (Turkey) have been analyzed by gamma-ray spectrometry to determine the specific activities of U-238, Ra-226, Th-232 and K-40 (Bq/kg). The natural radioactivity ranged up to 264 Bq/kg for U-238, 229.62 Bq/kg for Ra-226, up to 207.32 Bq/kg for Th-232 and up to 2541.95 Bq/kg for K-40. Any possible relationship between the specific activities of Ra-226, U-238, Th-232 and K-40 and some characteristics of the studied samples (age, rock-type, colour, grain size, occurrence, chemical and mineralogical composition) was investigated. Age, major and trace element geochemistry, color, pluton location and mineralogical composition are likely to affect the concentrations of the measured radionuclides. The range of the Th/U ratio was large (0.003-11.374). The latter, along with Ra-226/U-238 radioactive secular disequilibrium, is also discussed and explained by magmatic processes during differentiation.