In the present study two-dimensional open-channel flow with a side concavity having various plan shapes was investigated experimentally and numerically. In the experiments, surface and near bottom flow fields were measured using PIV technique and distribution of water depth and fluctuation of water surface was measured using a servo-type instrument. The numerical model is based on the finite volume method (FVM) with MUSCL scheme under unstructured grid system. The numerical results showed fairly good agreements with experiments for mean velocity distribution and mean water level variation within the side concavity. It was found from experiments that time dependent feature of water surface variation is closely related to the shape of the side concavity.