The decay resistance, hardness, water absorption, and thickness swelling of a bagasse fiber/polypropylene composite were evaluated. Brown- (Coniophora puteana) and white-rot (Trametes versicolor) fungal treatments were applied for 8, 12, and 16 weeks according to BS 838:1961 with the kolle-flask method. The brown- and white-rotted, and control composite samples were immersed in distilled water at 2 h and 24 h to measure the water absorption and thickness swelling of samples according to the ASTM D 570-98 requirements. Results indicated that the both lowest (3.2%) and the highest (7.2%) weight loss were observed in the white-rotted composite samples for 8 and 16 weeks fungal exposure times, respectively. The highest hardness (77.6 Shore D) was noted in the control composite samples, and the lowest hardness (65.5 Shore D) was recorded in the white-rotted composite samples. The highest water absorption (10.5%) was observed in the brown-rotted composite samples for 8 weeks fungal exposure time and after 24 h immersion in distilled water, and the lowest (3.8%) was noted in the control composite samples after 2 h immersion in distilled water. The highest thickness swelling (6.3%) was observed in the control composite samples after 24 h immersion in distilled water, and the lowest thickness swelling (1.9%) was found in the white-rotted composite samples for 16 weeks fungal exposure time and after 2 h immersion in distilled water.