This experimental study was conducted to evaluate the effect of polypropylene (PP) fibers added into pre-foamed ultra-lightweight composites (PULC) with a target dry density of 600 kg/m3. In this research, four PULC mixtures were designed with various PP fiber contents of 0, 0.4, 0.9, 1.4% by total weight of binder while other ingredients, including cement, fly ash (FA), slag, water, and stone powder, were kept constant. The dosage of foam and superplasticizer was adjustable to achieve the same target dry density and workability of the PULC mixtures. The PULC samples were prepared in the laboratory. After casting, these samples were stored at the room temperature condition until the required ages to implement to test. Engineering properties of the PULC samples, including compressive strength, the dry density, the water absorption, the drying shrinkage, the thermal conductivity, and the microstructure analysis, were tested to evaluate the performance as well as the potential application of such materials in reality. The experimental results show that for the specimen of 0.9% PP fiber content, the fiber addition helped to improve and enhance its compressive strength reaching the value within the range of 2.5÷3.2MPa. Furthermore, the thermal conductivity and the drying shrinkage decreased while the dry density gained a range of 639÷643 kg/m3. This research further indicated that 0.9% of PP fiber content was the optimal dosage and it also demonstrated a significant influence of the application PP fiber into the production of PULC.