In this paper, an experimental investigation of characteristics of developing turbulent steady flows in a square-sectional $180^{circ}$curved duct is presented. The experimental study using air in a square-sectional $180^{circ}$ curved duct carryed out to measure axials direction velocity and wall shear stress distrbutions by using Laser Dopper Velocimeter(LDV) system with data acquistion and processing the system of FIND6260 softwere at 7 sections from the inlet($phi=0^{circ}$) to the outlet($phi=180^{circ}$) in $301^{circ}$ intervals of a curved duct.