In this research, we have investigated the effects of addition of different percentages of nanoclay on the decay resistance and physicomechanical properties of natural fiber-reinforced plastic composites against white-rot fungi (Trametes versicolor). To meet this objective, the beech wood flour was mixed with polypropylene (PP) at 50% by weight fiber loading. The samples were prepared by melt compounding and injection molding. The concentration varied as 0, 1, 2, 3, 4, and 5 per hundred compounds (phc) for nanoclay. The amount of maleic anhydride-grafted PP (PP-g-MA) as a coupling agent was fixed at 2 phc for all formulations. Physical and mechanical properties of all the specimens were determined prior to and after incubation with the fungus for 8 weeks at 25°C and 75% relative humidity. Weight losses of the specimens were also determined after incubation. The results indicated that the flexural strength and modulus increased with an increase in nanoclay up to 3 phc and then decreased. However, the impact strength and water absorption were decreased with an increase in nanoclay loading. Furthermore, the lowest weight loss and the highest hardness were observed in the composite containing 5 phc nanoclay. The morphological findings showed that the samples containing 3 phc of nanoclay had higher order of intercalation and better dispersion.