In order to clarify the relation between the enhanced erythrocyte sedimentation rate in an inclined vessel and the medium upflow underneath the downward‐facing wall of the vessel, we have measured the upflow velocityValong the vessel lengthyand the width δ of the upflow layer at tilt angles θ of 10°, 20°, 40°, and 60°. Sample was a swine erythrocyte suspension at nonaggregated state at the volume fraction of 0.2. Polystyrene latex particles with 1‐μm diameter were mixed in the suspension to visualize the motion in the upflow layer. Observations were made with a video system under an invert microscope at room temperature. The upflow layer began to be formed immediately after the sample injection, and reached to the steady state within 10 min, while keeping a thin layer. The time for reaching the steady state decreased with increasing θ. The upflow velocity was much higher by two to three orders of magnitude than the sedimentation rate. BothVand δ increased with increasing θ. The observed velocity profiles were represented by the reduced equation 1−V/Vmax=(1−x/δ)2as predicted by the Acrivos and Herbolzheimer theory. Here,xis a coordinate taken along the end line at the bottom of the vessel.