Currently, petroleum-derived plastics are widely used. However, one of its main disadvantages is its low degradation time, which is not beneficial to the environment. Therefore, natural polymers are an alternative to overcome this obstacle. Among the natural polymers, starch can be highlighted. Thus, the objectives of our investigation were to obtain sisal nanofibers using low concentrations of acid solutions to produce and characterize corn starch nanocomposites reinforced with these nanofibers. The films were produced by a casting technique using commercial corn starch and glycerol as plasticizing agents; the nanofibers were obtained using acid hydrolysis. The films were subjected to tensile tests to evaluate their resulting mechanical behaviors. The results of X-ray diffraction and transmission electron microscopy analyses revealed the possibility of obtaining cellulose nanofibers using a sulfuric acid concentration lower than that previously reported in the literature. The nanocomposites reinforced with plant nanofibers showed lower tensile stress and elongation characteristics than the matrices without nanofibers.