Effects of fungal decay period on the technological properties of polypropylene/rice straw composites reinforced with different amount of carbon nanotubes (CNTs) were evaluated in this research work. The composite specimens were prepared using an internal mixer followed by compression molding. The specimens were then subjected to the fungal decay using white-rot fungus (Coriolus versicolor) for 1, 2, 3, and 4 months. The degree of fungal attack was recorded by determining the weight loss of the specimens. The physical and mechanical properties including water uptake, flexural strength, and impact strength (IS) were investigated. The results indicated that the weight loss of the specimens was significantly reduced by increasing the CNT loading levels. The weight loss ratio of the specimens with the CNT was lower than that of the specimens without the CNT. The modulus of rupture, modulus of elasticity, and IS of the specimens exposed to the fungal degradation increased in the presence of CNT. Furthermore, the decayed specimens without CNT had higher water uptake than those of the specimens with CNT. This was attributed to the decrease in the number of cavities on the surface of the composites containing CNT. Based on the findings obtained from the present study, it was concluded that the amount of the CNT should be considered according to the severity and duration of the fungal exposure.