Pembibitan kelapa sawit sering terkendala akibat pengelolaannya belum optimal, sehingga mempengaruhi  produksi  kelapa sawit. Salah satu kendala kelapa sawit adalah penyakit busuk pangkal batang disebabkan oleh Ganoderma boninense.  Pengendalian penyakit busuk pangkal batang diperlukan teknik yang tepat terutama pengendalian yang bersifat ramah lingkungan, seperti Trichoderma viride. Penelitian ini bertujuan untuk mengetahui kemampuan antagonisme jamur Trichoderma viride untuk menekan perkembangan Ganoderma boninense secara in vitro dan bibit tanaman kelapa sawit umur 7-9 bulan (main nursery). Penelitian ini dilaksanakan pada bulan Januari 2019 – Maret 2019 di Laboratorium Patologi, Entomologi dan Mikrobiologi dan di Lahan Percobaan Fakultas Pertanian dan Peternakan UIN Sultan Syarif Kasim Riau. Metode Penelitian ini menggunakan Rancangan Acak Lengkap (RAL) non faktorial dengan 4 perlakuan dan 5 ulangan. Hasil Penelitian menunjukkan bahwa aplikasi 25 g Trichoderma viride mampu menurunkan intensitas serangan Ganoderma boninense menjadi 22,90%. Sehingga pemberian dosis 25 g merupakan dosis yang efektif untuk menurunkan intensitas serangan Ganoderma boninense pada kelapa sawit umur 7-9 bulan (main nursery).   Elais guienensis Jacq seedlings in nursery main are often constrained due to less optimal management, affecting the oil palm production. One that opposes oil palm is a rotten disease caused by Ganoderma boninense. Control of stem rot disease requires appropriate suspended technique which is environmentally friendly, such as Trichoderma viride application. Trichoderma viride was applied to supress the development of Ganoderma boninense in in vitro and Elais guienensis Jacq seedlings aged 7-9 months (main nursery). This research was conducted in January - March 2019 at Pathology, Entomology and Microbiology Laboratory and at Experimental Field of Faculty of Agriculture and Animal Husbandry, UIN Sultan Syarif Kasim Riau. This research method used a non factorial completely randomized design with 4 treatments and 5 replications. The result proved that the application of 25 g of Trichoderma viride could supress up to 22.90% the development of Ganoderma boninense. Therefore dose of 25 g T. viride is more effective against Ganoderma boninense pathogen attack for Elais guienensis Jacq aged 7-9 months in main nursery.