The high consumption of polymeric materials, inefficient methods of disposal and the long degradation time of conventional polymers have aroused interest in the study and application of biodegradable polymers such as PLA. However, these polymers are known for their high prices. Reinforcing fibers could be incorporated to increase the market value of PLA. In order to improve mechanical performance are commonly added compatibilizers. However, their presence could lead to side reactions, like degradation. Therefore, additives that control these reactions may be added (hydrolysis stabilizer). In this study, PLA/sisal fiber composites (70/30) were prepared according to an experimental design, in which the compatibilizer and hydrolysis stabilizer contents were varied. The hydrolysis stabilizer is an additive which contains carbodiimide groups. Effects of the variables on the mechanical properties and morphology were assessed through tensile test and scanning electron microscopy, respectively. PLA degradation was assessed through size exclusion chromatography. The presence of both additives increased the tensile strength and decreased the modulus of the PLA/sisal fiber composite. Morphological analyzes of the composites indicate better adhesions in the presence of compatibilizer. When both additives were, simultaneously, incorporated in PLA/sisal fiber composites the tensile strength was also increased. In relation to the molar mass of neat PLA, the composites presented smaller average molar mass, however the increase of the acidity, due to addition of the compatibilizer to the composites, did not cause greater degradation to the PLA. In contrast, the hydrolysis stabilizing additive in upper level promoted an increase of the average molar mass of these composites. This result can be attributed to possible reactions between this additive and the carboxylicacid groups of both PLA-g-MA and PLA. Acknowledgements: FAPESP (Process: 2017/18678-4).