Abstract: Background and Objectives: Trichoderma spp. is a soil inhabitant fungus with an ability of inhibiting plant pathogens and immunity and growth enhancer in plants. Based on the available literatures, the objective of this investigation was planned to study the compatibility of Trichoderma harzianum along with two systemic and two non-systemic fungicides in vitro. Materials and Methods: To isolate the biocontrol agent i.e., T. harzianum from soil, soil samples were collected from crop fields of crop research centre (CRC) of SVPUA and T Meerut, India. Four fungicides viz Mancozeb, Thiram, Carboxin and Propiconazole at 25, 50, 75 and 100 ppm were tested for their compatibility with Trichoderma harzianum by poisoned food technique and inhibition (%) by individual fungicides were noticed and recorded at an interval of each 24 h. Data were subjected to analysis using appropriate statistical methods, analysis of variance and treatment means were differentiated using Fischer’s t-test in Completely Randomized Design (CRD) in laboratory. Results: It was evident that all the four concentrations of Mancozeb were highly compatible with almost negligible toxic effect against Trichoderma harzianum in vitro. As there was no or very little (0.00, 0.00, 5.19 and 7.03) inhibition of radial growth of Trichoderma harzianum due to Mancozeb at 25, 50, 75 and 100 ppm concentrations, respectively. Thiram was less compatible than Mancozeb. Carboxin and Propiconazole were toxic and incompatible with Trichoderma harzianum. Conclusion: Two non-systemic fungicides i.e., Mancozeb and Thiram were found to be compatible, as compared to systemic fungicides viz. Carboxin and Propiconazole which exhibited acute toxicity for growth of Trichoderma harzianum in vitro.