Because of the relatively high slenderness of castellated beams and significant area of the openings in the web, one of the possible failure modes is the lateral-torsional buckling. The simplified verification of the resistance for the lateral-torsional buckling is proposed in [1], which implies the similar calculation for the lateraltorsional buckling as for the standard plate beams but with the reduction of geometrical characteristics of crosssection. This calculation method uses geometrical characteristics of a cross-section through openings. It implies that the validation of lateral buckling resistance is the same for a castellated beam and standard plate girder but with the reduction of the castellated beam cross-section geometrical characteristics. The aim of this research is to show procedures for the calculation of the critical moment for the castellated beams, using FEM and expression given in [1], in order to determine the influence of the reduced geometrical characteristics of the castellated beams in relation to the plated beams with the same cross-section dimensions.