In recent years there has been great technological progress in the development of composite materials reinforced with natural fibers. This increase in interest from industries and research groups in developing and using materials made from renewable materials is mainly due to the worldwide call for environmental preservation. The aim of this study was to characterize composites reinforced with treated sugarcane bagasse fibres in a high-impact polystyrene (HIPS) matrix, with the aim of possibly replacing the materials currently used in the pet shop industry. Three families of composites were characterized, in proportions of 10, 20 and 30% (m/m). The composites were characterized using the techniques of helium pycnometry, Shore A hardness, impact resistance and fluidity index. The addition of bagasse fibers to HIPS resulted in a material with up to 30% less polymer and with viable mechanical properties for certain HIPS applications, where cost and Shore A hardness are more important than impact resistance.