Purpose: Aim: This study was designed to determine the effect of fiber reinforcement on the fracture strength and toughness of long span provisional restorations. Materials and method: Two types of commercially available provisional materials were selected: Protemp™ II and Protemp™ 4. A number of twenty samples were made for each material. The samples of each group were further subdivided into two equal subgroups (A and B); where subgroup A served as control, without fiber reinforcement while subgroup B included the addition of ultrahigh modulus polyethylene fibers (UHMPE) which is delivered pre impregnated by the manufacturer. The fibers were pre weighed using an electronic scale, and cut to a predetermined length (2-3mm) before incorporation in the resin mix to represent 3% weight of the control sample. Two sample designs were selected according to the requirements of testing: Twenty 4 unit fixed partial dentures for fracture strength test (D 1), and twenty rectangular specimens for fracture toughness test (D 2). The specimens were left in saline for 7 days before testing. Conclusions: Protemp™ 4 presented higher fracture mean values than Protemp™ II. For the two types of specimens, although the result didn’t shown a significant increase in the fracture strength and toughness values of the reinforced resin, however, reinforcement prevented total separation of the fractured parts and held the fragments together.