This study aims to investigate the effect of novel high-strength polyethylene fibers on the unconfined compressive strength (UCS) behavior of concrete produced with admixed Bangkok clay cement. Bangkok clay samples were prepared at a liquid limit of 88% and were added to ordinary Portland cement (OPC) at 2, 4, 6, 8 and 10% by weight; polyethylene fibers were also added at 0.5, 1.0, 1.5, 2.0 and 2.5% by volume. These samples were cured for 7, 14, and 28 days and subjected to an unconfined compressive test. From the test results, the cement content of 8% by weight was the optimum, and a polyethylene fiber content of 1% by volume is recommended. Moreover, the novel high-strength polyethylene fiber with 0.2 mm in diameter and 6 mm in length provided the maximum UCS value.