This paper presents the experimental results on the simply supported PFRP channel beams subjected to three-point loading. The objectives of the research work are to investigate the effects of the span (L) of the beams on the behaviors, the critical buckling moments and the modes of failure of the beams, and to compare the obtained critical buckling moments with those obtained from the modified LFRD steel design equation in order to check the adequacy of the equation. The beam specimens have the cross-sectional dimensions of 102×29×6 mm with span-to-depth ratio (L/d) ranging from 20 to 40. A total of ten specimens were tested. Based on the test results, it was found that the load versus mid-span vertical deflection relationships are linear up to the failure, but the load versus mid-span lateral deflection relationships are geometrically nonlinear. The general mode of failure is the flexural-torsional buckling. Finally, the modified LFRD equation can satisfactorily predict the critical buckling moment of the PFRP beams used in this study.