In this study, antimicrobial activities of different plant samples were tested against Trichoderma harzianum and Pseudomonas agarici, which causes disease green mold and yellow blotch in mushroom respectively. For this more than 100 plant leaf samples were collected from different regions of eastern Uttar-Pradesh like Varanasi, Mirzapur, Chandauli, Chunar, Jaunpur and Gorakhpur. Some of these plants are used for the treatment of various ailments by the indigenous population. The antimicrobial activities were evaluated according to the poisoned food technique using aqueous and alcoholic extract of the leaf samples against both, the test fungus and bacteria. In the end of the experimental studies the plants such as; Psidium guajava, Polyalthia longifolia, Andrographis paniculata, Ocimum sanctum, Jatropha sp, Parthenium hysteroporus, Ficus religiosa etc. leaf samples were found to be effective against the fungus T. harzianum. On the other hand the plant extracts of Ricinus communis, Parthenium hysteroporus, Syzygium cumuni, Emblica officinalis, Woodfordia floribenda, Polyalthia longifolia, Andrographis paniculata, Euphorbia hirita and Nerium indicum were found to be effective against the bacteria P. agrici. We are reporting about antifungal as well as antibacterial property of some plant extract against Trichoderma harzianum and Pseudomonas agarici.