This study aims to valorize composted olive pomace as a culture substrate for the growth and development of the fungus Trichoderma Harzianum, which is a very useful biological control agent in Agriculture for rapid growth and good biomass yield compared to other culture media (PDA and Czapeck- Dox) often used for mushroom production. The results of physico-chemical analyses showed that composted olive pomace has a pH favorable to Trichoderma harzianum development, contains less cellulose and is richer in mineral salts than fresh olive pomace. A comparative study of Trichoderma harzianum mycelial growth on different culture media (composted olive pomace, pure PDA, Czapeck-Dox, PDA and olive pomace, Czapeck- Dox and olive pomace, PDA olive pomace and coffee grounds, Czapeck- Dox olive pomace and coffee grounds) showed that after 6 days incubation, natural media based on composted olive pomace and potato (PDA) proved to be the most suitable for growing Trichoderma harzianum, given the complex compounds that make them up, compared with synthetic media (Czapeck- Dox), which are less conducive to the growth of this fungus. However, the results of this study clearly showed that the composted olive pomace-based culture medium gave the best results in the growth of Trichoderma harzianum.