In this study, authors have investigated on the laws of resistance to flow in vegetated channels for the purpose of settling the limits to luxuriance of vegetation in a channel. Experiments were performed in flumes having rigid roughness and flexible roughness, which were imagined as wooded and grassed channels respectively. The main results are follows; (1) The velocity distribution is formularized by the two logarithmic expressions showing distinct gradients, and also in case the relative depth is comparatively large the logarithmic formula by Prandtl-von Karman holds good for the rough turbulent flow. (2) The value of the relative depth at which the gradient of distribution curve varies, appears to be a function of roughness concentration λ. And the value of Ar in the expression of velocity distribution is a constant for given roughness concentration λ and channel slope I. (3) When the roughness is bending as in grassed channels, the deflected height of the roughness elements can be dynamically estimated by the drag force obtained from integrating the logarithmic velocity distribution. (4) The equation of the mean velocity for quasi-wooded and quasi-grassed channels are represented by Eq. (20), (21).