Biocomposites containing natural fibers waste have gained the attention of researchers due to their biodegradability and suitability for several applications in different industries. In this study, sugarcane bagasse fibers waste was treated by digestion with NaOH and steam explosion to the previous soaking with NaOH, and their impregnation with 1% maleated polyethylene was used as reinforcement in poly (lactic acid) matrix composites. Surface morphological changes were observed with scanning electron microscopy due to fiber treatment/MAPE in the PLA matrix. The biocomposites with MAPE improved Young’s modulus, but the strength tensile was reduced. Flexural modulus of biocomposites shows a considerable increase with MAPE, for biocomposites of 10% and 20% of bagasse the values are circa 8000 MPa regarding the 3500 MPa from PLA. These increases in the properties are ascribed to the improved interfacial interaction of the modified sugarcane bagasse fibers into the PLA. The analysis of TGA shows that incorporation of fiber with and without treatment and MAPE improved the thermal stability. By adding fiber into the biocomposites, the loss modulus peak becomes wider, this means that adhesion of the matrix and the fiber were improved. The X-ray diffraction graph shows an increase in the crystallinity of the biocomposites after the treatment and the addition of MAPE compared to the matrix of PLA.