Effects of walls on shedding vortex in developed channel flow were investigated putting a cylinder a t the center of channels or on a wall for the value of wld from 2 to 4. Results were compared with the uniform flow result.When a cylinder was put at the center of the channels, non-dimensional frequency plotted against Reynolds number agreed with the uniform flow result a t low Reynolds number. However, i t increased rapidly with Reynolds number, then it lay considerably above the uniform flow results a t high Reynolds number. When a cylinder was put on a wall, nondimensional frequency was considerably lower than the uniform flow result in the cases Of wld=3 and 4. In the case of w J d = 2 , however, frequency was higher than the uniform flow result a t high Reynolds number. In all cases in the present study, the transition Reynolds number increased with decrease in the value of wld.These results indicate that the increase in shedding frequency was due to the shift in velocity distribution from Poiseuille parabora in the wake region, which obviously increased with Reynolds number and with decrease in channel width.