Abstract: This study was to compare the flexural strength of three types of glass-ionomer cement combined with two types of fibers. About 90 specimens were prepared in a split mold. Glass and polyethylene fibers measuring 1 mm in length were added to the powder of Conventional Glass-Ionomer cement (CGIc), a Resin-Modified Glass-Ionomer Cement (RMGIc) and cermet (miracle mix). The specimens were divided into 9 groups according to the type of glass-ionomer cements and the fibers (n = 10): Group 1: CGIc; group 2: RMGIc; group 3: Cermet (MM); group 4: CGIc + glass fiber; group 5: RMGIc + glass fiber; group 6: MM + glass fiber; group 7: CGIc + polyethylene fiber; group 8: RMGIc + polyethylene fiber; group 9: MM + polyethylene fiber. The mean flexural strength (MPa) values were determined in a 3-point bending test at a crosshead speed of 0.5 mm min-1 by a universal testing machine. The results were analyzed using two-way ANOVA and a post hoc Tukey test (p<0.001). Flexural strength increased significantly after adding 8 glass or polyethylene fibers to GI cements (p<0.001) except when glass fibers were added to cermet (p>0.001). In addition, flexural strength of polyethylene fibers increased more than that of glass 3 fibers in all the groups (p<0.001). Adding fibers, especially polyethylene fibers can increase flexural strength of glass-ionomer cements.