In the present study, flow characteristics of turbulent pulsating flow in the square-sectional $180^{circ}$curved duct are investigated experimentally. In order to measure axial direction velocity and secondary flow distributions, experimental studies for air flow are conducted in the square-sectional $180^{circ}$curved duct by using the LDV system with the data acquisition and the processing system of the Rotating Machinery Resolver (RMR) and the PHASE software. The experiment is conducted on seven sections form the inlet($phi=0^{circ}$) to the outlet($phi=180^{circ}$) at $30^{circ}$intervals of the duct. The results obtained from the experimentation are summarized as follows : In the axial direction velocity distributions of turbulent pulsating flow, when the ratio of velocity amplitude (A1) is less than one, there is hardly any velocity change in the section except near the wall and in axial velocity distribution along the phase. The secondary flow of turbulent pulsating flow has a positive value at the bend angle of $150^{circ}$regardless of the ratio of velocity amplitude. The dimensionless value of secondary flow becomes gradually weak and approaches zero in the region of bend angle $180^{circ}$without regard to the ratio of velocity amplitude.