Viscoelastic flows are studied experimentally using two‐dimensional L‐shaped channels. Velocity and pressure distributions have been measured for various flow rates and for various channel widths on the downstream side in order to clarify the causes and the conditions under which a reverse flow is generated upstream of the re‐entrant corner. The present experiment shows that the reverse flow is a maximum in extent when the mean velocity and the channel width downstream of the re‐entrant corner are varied. Pressure distributions on the channel wall rise in the flow direction in the upstream vicinity of the re‐entrant corner. This pressure rise is a maximum in magnitude and in extent under the same conditions as the reverse flow. The Weissenberg effect, peculiar to viscoelastic fluids, may be the cause of the reverse flow and the pressure rise upstream of the re‐entrant corner.