An experimental investigation was performed for the pulp-suspension flow in a duct, which is an extremely simplified model of a hydraulic headbox of paper-making machines. Flow visualization and optical measurements of the fiber concentration were made in the wake region of a flat plate. Characteristics of pulp-suspension flow were examined for five cases of fibers behavior appeared in the passages partitioned by the plate. A discussion is given on the time-averaged and the fluctuating fiber-concentration and on the flocculation and the breakdown of the fiber network.