Purpose: The intention of the current in vitro research is the effect of different modifications to U-shaped maxillary major connector design on rigidity, using load deflection.Materials & methods: The intention of the current in vitro research is the effect of different modifications to U-shaped maxillary major connector design on rigidity, using load deflection. Three chrome cobalt alloy frameworks were fabricated from the same master cast for each four different U-shape maxillary major connector designs. The designs were "8 mm" wide U-shaped strap of "0.5 mm" thickness, "8 mm" wide U-shape strap of "1.1 mm" thickness, "17 mm" wide U-shape strap of "0.5 mm" thickness (3 planes design), and "8 mm" wide anterior U-shaped and posterior strap "0.5 mm" thickness (anteroposterior). Loading points were marked on each framework corresponding to the left first molar position. Reference points were determined and notched at each side of the frameworks. Frameworks were then seated at a previously fabricated Kennedy class III modification 1 acrylic model that simulated bone and oral mucosa. A vertical "300 N" load with a "2 mm" cross-head was applied to the loading point by a universal testing machine for 3 minutes. Measurements were taken and recorded before and during loading period. Results: Results of the present study showed a statistically significant difference in the comparison between overall percentage changes in the four groups. Group I "a" (0.5 mm thickness design) showed the most percentage change in dimension. Group I "b" (1.1 mm thickness design) showed the least percentage followed by Group III (Anteroposterior strap design). Group II (3 planes design) showed less percentage change in dimension than Group I "a" (0.5 mm thickness design). Conclusions: Within the limitations of this study, the thickness and design of the maxillary major connectors affect rigidity, where the following was concluded: 1) 1.1 mm thickness (U-shaped) palatal strap showed the most resistance to deflection on torsional loads. 2) Anteroposterior major connector showed less resistance to torsional loads followed by the 3 planes design and the "8 mm'' wide U-shaped design respectively.