In this paper we describe a study of the durability of calcium aluminate cement (CAC) reinforced with nano- and micro- cellulose fibers. The nanocelluloses were in the form of nanofibrillated cellulose -obtained from sisal pulp by the application of a high intensity refining process- or as nanocrystals –obtained from acid hydrolysis of pure microcellulose. The setting time (Vicat), strength development (flexural strength), and durability to aging (wet/dry cycles and scanning electron microscopy analysis) were studied. The results have show that the presence of fibers in the matrices modifies the setting times towards reducing them; the mechanical behavior was found better in the fiber CAC matrices compared with CAC mortars. Regarding the durability tests, CAC cementitious systems keep intact the mechanical properties of the fibers. SEM photographs of fracture section show the surface of the fibers with very little state of degradation. These results would indicate that the absence of calcium hydroxide prevents the chemical degradation of cellulose.