Abstract: Trichoderma harzianum Th3 was inoculated on the spentsubstratefrom Pleurotus eryngii cultivation for fermentation. The resulting material wassubsequently mixed with the greenhouse soil at 5levels to evaluate their effects on the soil through observations on the growth of Brassica campestris planted on them. The pH, invertaseand urease in the soil mixture, the Th3countinrhizosphere, as well as the germination, emergence, total biomass, and chlorophyll content of the vegetable were determined. The results showed that the ratio of Th3 preparation to soil at 1:39 resulted in significant increases onthe seedling emergence (83.93% at maximum), the leaf chlorophyll content by 51.23%, thetotal biomass by 27.94%, the soil pH to 6.97, the invertase activity to 8.80 mg·g^-1-d, the urease activity at 2.21 mg·g^-1-d, and the enhancement of Th3 count in the rhizosphere. It appeared that addition of theTh3 preparation using the spent substrate from mushroom cultivation could improve the soil quality and yield of B. campestris.