The acai fruit industrial processing produces a large amount of waste, mainly seeds and fibers, which is a serious environmental and public health problem. The objective of this work was to use these fibers to obtain composites with natural rubber from different clones. The effect of the addition of acai fibers and the type of clone were investigated using thermogravimetric analysis (TGA) under inert and oxidative atmospheres, differential scanning calorimetry (DSC), water sorption, and mechanical properties. The acai fibers exhibited a thermal behavior comparable to other natural fibers industrially used in polymeric composites. The addition of the fibers did not influence the thermal stability of the composites. There was no significant effect of the type of clone and the addition of the fiber on the glass transition temperature, which was approximately -59 degrees C for all samples. Water sorption behavior of the compounds and of the composites was similar to that of the other materials with natural rubber that are reported in the literature. The promising performance of the composites with acai fibers opens a new area of use for such fibers.