This research analyzes the effects of the previous wetting and drying treatments of cellulosic fibers on the fiber–matrix bond strength of cement based composites. First, three kinds of fibers—abaca, cabuya and sisal—were subjected to five cycles of water wetting and subsequent drying. The resulting changes in the morphology, mechanical properties, drying kinetics and thermal stability were determined with scanning electronic microscopy (SEM), tensile tests and thermogravimetric analysis (TGA) respectively. A reduction in the cross section, an increase in Young’s modulus and adecrease in tensile strength and tensile strain as well as a structure with thinner pores was found for the treated fibers. Second, cement based composites with untreated and treated fibers were prepared to evaluate the fiber–matrix bonding before and after accelerated aging. For this purpose the interfacial shear strength (IFSS) between the fibers and the matrix was determined by the single fiber pull-out test after seven days of curing in a humidity chamber and after four aging wetting–drying cycles. The treatment of the fibers results in an increase in the interfacial shear strength of the cement composites also improving the durability