Natural fibers are widely used ecological materials, mainly in civil construction, where they can be inserted into cement matrices, among other applications. One of these natural fibers is coconut fiber and its use in cement composites presents several benefits. The fibers provide better mechanical properties to concrete because they have higher tensile strength and modulus of elasticity than the cement matrix. The fibers absorb the load, increasing the residual strength of the composite. As disadvantages, they have greater variability of physical and mechanical properties, lower durability, low resistance to microbial attacks and low resistance to moisture. However, these problems can be minimized by modifying the fiber surface through chemical and physical treatments. Thus, this article aims to analyze the performance of cement composites with coconut fibers subjected to mercerization and hornification treatments through flexural tensile strength testing and scanning electron microscopy (SEM). From the results found, it was verified that the mercerization treatment applied presented better results when compared to the hornification treatment, presenting a rougher, cleaner and more uniform surface, which helped in the interface with the composite. In addition, it also presented a higher proportionality limit and residual resistance, which for application in cementitious composites is interesting because in the post-cracking behavior the fibers serve as a bridge for transferring stresses through the cracks.