Purpose: The purpose of this study was to evaluate the effect of different marginal designs on the fracture strength and marginal accuracy of interim fixed partial dentures made of three different materials fiber reinforced composite.(Targis vectris), Bis acryl composite(protemp п) and polymethyl methacrylate(Vertex). Materials and methods: Thirty standardized 3- unit provisional fixed partial dentures were fabricated using stainless steel dies and standardized plastic models then divided into 3 equal groups: Group A was fabricated from fiber reinforced composite (Targis vectris).Group B from ,Bis acryl composite(protemp п) and group C from polymethyl methacrylate(Vertex). Each group was furtherly subdivided into 2 subgroups according to the marginal desin (shoulder or chamfer finish line). The FPDs were successively luted on the metal dies using eugenole free temporarily cement .Marginal adaptation test was performed using stereo microscope and fracture resistance test was performed using Insteron testing machine. Scanning electron microscope was performed to study the mode of fracture. Results: Two-way Analysis of Variance (ANOVA) was used in testing significance for the effect of material, finish line and their interactions on marginal accuracy and fracture resistance. Tukey’s post-hoc test was used for pair-wise comparison between the means when ANOVA test is significant. The significance level was set at P ≤ 0.05. The results showed that material and the interaction between the two variables had a statistically significant effect on mean marginal accuracy. Finish line had no statistically significant effect on mean marginal accuracy. Concerning the fracture resistance, The results showed that material, finish line and the interaction between the three variables had a statistically significant effect on mean fracture resistance Conclusion: Fiber reinforced composite with Shoulder finish line was the best in marginal accuracy. While, Bis-acryl composite was the worst. The highest fracture resistance was significantly performed by Targis Vectris provisionals especially those constructed over chamfer finish line.This was followed with protempп bridges