Diseases caused by Ganoderma spp. have been causing serious oil palm yield losses and affecting its contribution to the producers’ economy. Research on sustainable and eco-friendly remedy to counter the disease is on the upsurge. Trichoderma spp. have been the most studied and valued microbes as biological control agents (BCA) in an effort to combat a wide range of plant diseases. Therefore, in this current study, the potential of Trichoderma spp. ( Trichoderma asperellum, Trichoderma harzianum, and Trichoderma virens) as a mixture was evaluated as a BCA against basal stem rot disease of oil palm. The mixture of Trichoderma spp. demonstrated a disease reduction of 83.03% and 89.16% from the foliar and bole symptoms, respectively. The highest peroxidase (PO) level was detected in T1 (167.9 U g^-1 tissue) at four months after post inoculation (mpi), and the lowest in T5 (72.3 U g^-1 tissue) at 1 mpi. Treatment 4 with all the three Trichoderma spp. displayed the maximum level of polyphenol oxidase (PPO) among all the treatments conducted. Similarly, T4 recorded the highest accumulation of total phenolic content (TPC) (49.6 mg g-1) in the seedling roots at harvest. Disease infestation was slower in Trichoderma treated seedlings regardless of a single or mixture application compared to the positive control.