The fundamental bending strength characteristics of channel section beams are studied by a numerical analysis and checked with respect to the effects of loading conditions, type of cross sections and initial imperfections. The slender type of high depth channel to be likely used in plate girder structures and the compact section type for hot-rolled shapes are adopted here. Mainly emphasized are the effects of prevention of twist at the loading point and the warping restraint at beam ends. The reduction of bending strength due to lateral-torsional buckling is significantly improved by the end warping restraint and prevention of twist at the loading point. Finally, it is concluded that the channel section beams can be used as main structural members.