This paper presents the results of an experimental investigation on the behavior of T-shaped RC beams with rectangular web openings under pure torsion. Seven beam specimens were tested to study the influence of geometrical parameters on the torsional strength. The investigated parameters were: (1) the flange width, (2) the flange thickness, and (3) the opening height. All specimens had the same span, depth, web width, and opening length. All beams were loaded till failure. Cracking patterns were monitored and systematic measurements were taken to draw the torque-angle of rotation curves. The results are analyzed to study the effects of the studied parameters on the cracking torque, the ultimate torque, the angle of rotation at cracking, the angle of rotation at ultimate, and failure modes. The analysis of testing results highlights several key aspects to provide a set of recommendations for such beams. The experimental results show that the geometrical parameters (flange width, flange height, and opening height) profoundly affect the behavior of T-shaped RC beams under pure torsion. A new analytical model based on the softened truss model has been used for predicting the torsional behavior of the tested beams. The softened truss model has been successively used for torsion, which is extended to T-shaped RC beams with large web openings under pure torsion. The analytical torque-rotation curves were compared with the experimental ones and observations were noted.