Objectives: It has been widely accepted that rigidity is one of the desirable characteristics of removable partial dentures major connectors. The aim of the research was to investigate the effect of lingual bar major connector design on flexing and torque resistance by means of three-dimensional finite element analysis. Methods: Eighteen designs of lingual bars of different cross-sectional shapes and dimensions (4-5mm height, 1.5-3mm thickness, 0.3-0.75 thickness/height ratio) were developed using finite element analysis modeling. Half-pear and half-oval shapes with different cross-sections (5.88-10.59 mm²) were constructed for comparison. Vertical and horizontal forces of 30N were applied to one end of the bars, while the opposite side was fixed in all directions. The rigidity of the experimental Co-Cr major connectors was evaluated by measuring relative displacements and von Mises stresses generated under simulated torsional and compressive loads. Results: Stresses and displacements for compression loading simulating vertical forces were lower than those obtained for torsional loading simulating horizontal forces (61-63% for stresses and 41-74% for displacements). The displacements for compressive loading became closer to them for torsional loads with the decrease of the thickness/height ratio. Resulted displacements and stresses were smaller for bars with an increased thickness/height ratio. Values measured for half-oval designs were not significantly higher than those for the half-pear shapes. Conclusion: The results of this in vitro study suggest that the thickness of the lingual bar major connector should be increased to improve the rigidity of the framework to torsional and compressive loads. Cross-section shapes of the lingual bars have a lesser effect on rigidity as biomechanical point of view. (Grant: CEEX 2978/11.10.2005) Keywords: removable partial denture, three-dimensional finite element analysis, lingual bar design