The effect of synthetic fibers on the flexural performance of clay and sand mixtures treated with cement has been investigated through a flexural performance test with a third-point loading. Flexural test beams were fabricated with a various amount of bentonite, cement, river sand, and synthetic fibers. Bentonite in lieu of clayey soils was employed in the experiment. The X-ray diffraction analysis on the bentonite revealed that its main components were clay minerals such as montmorillonite and illite. Two types of fibers, PVA (Polyvinyl alcohol) fibers and PP (Polypropylene) fiber, were employed in the experiment. The test results have exhibited that the factors considered in the tests have significant effects on the flexural performance of bentonite-cement mixtures in several aspects. The brittle behavior of bentonite-cement mixtures has been improved into the ductile behavior due to the inclusion of fibers. The increase in the flexural strength of bentonite-cement mixtures has been attributed to the addition of sand. A multiple linear regression analysis has been performed to evaluate the effect of fiber content and fiber length, cement dosage, and sand content on the flexural performance of mixtures in terms of flexural strength, residual strength, and flexural toughness. Cement dosage and sand content were estimated as important factors to have an influence on the first-crack strength and the ultimate strength whereas fiber content has the most significant influence on the post-crack behavior. The first-crack strength and the ultimated strength were increased as the cement dosage and the sand content were increased. As the fiber content was increased, the residual strength and the flexural toughness were increased. A paired t-test has also been peformed on the test results to evaluate the relative superiority of fibers employed in the test. The 12mm-long PVA fiber showed the best performance to improve the flexural strength, the residual strength, and the flexural toughness of mixtures.