Sugar cane bagasse (SB)–low density polyethylene composites with different mechanically treated SB were prepared by a melt compounding method. The effect of the different treatments using supermasscolloider at low content of SB on the morphology, mechanical properties, and thermal behavior was investigated. Scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy indicated that the dispersion, crystallinity, and bonding of SB fibers depend on number of the treatments. The high modulus of SB generally improved tensile modulus of low-density polyethylene linearly and is proportional to supermasscolloider treatments. All composites show that the elongation at break was fairly constant within experimental error. Thermal stability decreased in the presence of SB and linearly increased in respect to the treatment times. The melting temperature decreased at lower passes. However, at higher passes, there was a marginal change. POLYM. COMPOS., 38:1497–1503, 2017.