Abstract. The present study was planned to evaluate the efficiency of potential antagonistic Trichoderma as biocontrol agent for damping-off of tomato and root rot of kidney bean plants, by optimization of cultural factors of Trichoderma in soil under laboratory conditions. Results revealed that inoculating Trichoderma into the soil as mycelial preparations grown on rice husks, resulted in better survival and proliferation, than when grown on corn meal at concentration of 5 % with soil moisture content of 30 % WHC and optimum temperature 28°C. The incubation period of 12 days and pH of 5.5 resulted in best dry weight and the best antagonistic potential. The optimum incubation temperature that gave the highest dry weight was 25°C while that gave the best antagonistic potential was 20°C. Using chitin and sodium nitrate as carbon and nitrogen sources induced growth and best antagonistic potential. Key words: Antagonistic effect, Trichoderma harzianum , Pythium ultimum, Macrophomina phaseolina, Rhizoctonia solani, Sclerotium rolfsii.