An experimental study was carried out to elucidate the flow characteristics around the louvered fins used in a radiator and condensor for motorcars. The flow velocity and pressure distribution around an inclined forward facing step, imagined as a louvered fin, were measured in a duct as a parameter the flow rate in downstream of the step. Flows around the inclined forward facing steps of the two kinds of 90° and 30° were examined using the fiberoptic Laser Doppler Velocimeter(FLDV) and flow visualizing method by dye injection. The flow which goes over the step forms a recirculating zone just behind the step due to flow separation. The flow through the opening part just near the step is passably obstructed by a slow-moving vortex occuring in the opening part. The reattachment point length of the step which the opening part is closed, is obtained from flow velocity measured by FLDV.