Abstarct: Cylinder aerodynamics has been studies for over 100 years. The incompressible, viscous flow around a circular cylinder is a classical problem in fluid mechanic. impact of the Reynolds number, free stream turbulence, blockage and rotation on the flow past a circular cylinder reported in the thesis. In this investigation was used hotwire technique to measure velocity distribution. experiments were performed using the open wind tunnel of 40×40 cm in section and 168 cm in length. The model used was a cylinder of diameter D= 2 cm. the experimental instrumentation available at the aerodynamics laboratory of university of sabzevar. the Reynolds number rang covered is from about 5900-30680. the present results indicate that increase of rotating and free stream turbulence and decrease of blockage ratio and the Reynolds number lead to decrease coefficient drag.