An investigation was conducted to study the effect ofloading level with respect to shear center and span length onlateral torsional buckling of steel I-section beams using linearand nonlinear finite element analysis available in ANSYS(version 12.0) computer program. The steel beams which havebeen studied included prismatic beams and linearly web tapered beams with web tapering ratio of (0.5). The maximumheight of all beams was 300 mm with span length of 4, 6 and 8m. The critical buckling loads for prismatic and linearlytapered cantilever and simply supported beams subjected topoint load and uniformly distributed load were determined.The results showed that the bottom flange loading gives abuckling loads higher than that of the top flange loading withpercentage increases of 148% and 155% for the linear andnonlinear analysis respectively for the prismatic beams. Whilefor the tapered beams, these percentages increases were 61%and 67% respectively