The main objective of this study is to optimize the modulus of rupture of fiber-reinforced cement composite using a factorial design experiment. For that, pressure and time of the autoclave process, amount of aluminum hydroxide, and the cement/silica ratio were varied with two levels. The optimization aimed was to determine the influence of each of these factors on the modulus of rupture (MOR) of the samples to determine the optimal levels that maximize the bending strength through the response surface methodology (RSM). The structural and morphological properties of the fiber-reinforced cement composites were studied by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The obtained results suggest that mineralogical phases present in the composites were independent of the factors and the levels of the experimental design. In contrast, morphological changes were observed in the samples because of the interactions between fibers with the cementitious matrix. The most significant variables in the experiment were the cement/silica ratio and the pressure of the curing process in the autoclave. The increases in the cement/silica ratio and the reduction in the pressure of the autoclave process improve the bending strength. The increases in pressures and the curing time produce an excessive crystallization of its components generate a decrease in the modulus of rupture of the compound. For a curing time of 8 h, the modulus of rupture was reduced, since there is not enough time to achieve the highest conversion of C2SH to tobermorite. Investigating the effect of process variables on the properties of fiber cement slabs is of great importance in the construction industry since it leads to the optimization of their production and manufacturing, which allows improving the cost-performance ratio.