We obtained the shear velocity structure of NW Iran and its surrounding areas to a depth of 160 km using the nonlinear inversion of Rayleigh wave dispersion curves. Our results indicate that the crust in the south Caspian basin consists of three layers, a thick sediments and a granite upper crust over an oceanic-like crust that has been extended beneath Talesh Mountains. We obtained the lowest thickness of the lithosphere and the lowest shear velocity in the lower crust in eastern Turkey. The lowest thickness of the crust was observed in Zagros folded and thrust belt, while there was a thickening both in the crust and in the lithosphere in the Sanandaj-Sirjan zone comparing its two sides, so that the greatest thickness of the crust and lithosphere was observed in this area.