This paper presents experimental visualization results of airflow in rear of blades of dampers installed in duct systems and measurement of pressure differences between upstream and downstream of blades for parallel and opposed-blade dampers. Rear flow of damper blades is visualized using the smoke wire method with liquid paraffin. Pressure differences between the upstream and downstream of damper blades were measured with Pitot tubes and a micropressure gauge in accordance with ISO7244-1984. We compared flow fields aft of blades for parallel and opposed-blade dampers. Good agreements are made between numerically simulated results and experimental results. An opposed-blade damper is appreciated more favorably than a parallel-blade damper in view of less uneven flow aft of blades and the controllability of pressure drops for a duct system.