This study aims to investigate the long-term mechanical properties and durability of cementitious composites (CC) with low polypropylene (PP) fiber content and local river sand. The CC samples were prepared with different water-to-binder (w/b) ratios (0.20, 0.25, and 0.3), low PP fiber content (0.6% by mass of binder), locally available river sand, and fly ash (FA) sourced in the Mekong Delta region, corresponding to the mixture name WB20, WB25, and WB30, respectively. Then, the mechanical properties were investigated through compressive and flexural strengths and ultrasonic pulse velocity tests, while durability was assessed via chloride ion penetration and sulfate resistance. The results revealed that the mixture with the w/b of 0.25 achieved the best performance in terms of both mechanical and durability performance due to the optimal conditions of compaction, mixing water content, and also the latent pozzolanic reaction of FA in the hydrated cementitious composites. Besides, the CC samples with 0.6% PP fiber exhibited ductility behavior under compression and flexure, characterizing that CC samples do not completely separate from each other when damaged due to the fiber bridging effect. Moreover, the CC samples obtained excellent long-term durability (up to 120 days old) in terms of sulfate attack and chloride resistance in the following order WB25 > WB20 > WB30. The results of this study confirm the applicability of the local materials for producing good quality and low-cost cementitious composites.