The presence of aquatic vegetation in irrigation canals retards water flow through additional drag force. The aim of this study is to present the impact of water hyacinth on flow velocity profile and drag coefficient in irrigation canals. To achieve this aim experimental program was carried out in a circulating water flume, using water hyacinth. Four different vegetation densities, three different vegetation root depths and three different vegetation zone lengths were used with smooth and rough channel bed. The case without water hyacinth was considered as comparative case. It was found that, for the case without water hyacinth, vertical velocity profile was resembled for theoretical logarithmic distribution in open channel. For the case with water hyacinth velocity vertical profiles became close to the theoretical velocity distribution in a closed conduit but did not reach zero at water surface. Also vegetation density, vegetation root depth, vegetation zone length and bed roughness have a significant effect on the position of maximum velocity. Also the vegetation drag force increases by increasing vegetation density, vegetation root depth and vegetation zone length. In addition, equations were deduced using multiple linear regression analysis to calculate vegetation drag force for both smooth and rough flume bed.