Use of steel girders with web openings in constructing floor beams of building structures and footbridges is becoming more popular due to their cost effectiveness compared to the labor-intensive lattice construction or conventional solid web sections. Despite the fact that the increase in the height of the section due to web openings leads to significant enhancement in its flexural strength, the discontinuity in the girder cross-section due to the presence of web openings may affect the girder load carrying capacity. This may occur in the particular failure mechanism in which the girder fails by lateral distortional buckling prior to the attainment of its full flexural capacity. In the lateral distortional buckling mechanism, and as a result of the variation of the bending moment along the girder axis, the strength of the girder is highly influenced by themoment distribution along the girder's longitudinal axis. In the current study a three-dimensional finite elementmodel is developed to investigate the flexural-torsional behaviour of girders with circular web openings under various loading conditions. Numerical analysis is conducted to determine the critical buckling moment of perforated girders and the corresponding buckling mode. The impact of girder slenderness and web openings size on the moment carrying capacity is also examined. Recommendations are provided for the applicability of the moment gradient formula of conventional sections for sections with circular web openings.