An in vitro experiment was carried out to evaluate the effectiveness of antibiotics at different concentrations on growth and development of Trichoderma harzianum, Phytophthora infestans, Colletotrichum gloeosporioides, Corticium theae and Fusarium oxysporum found in tea plantation. Three samples viz. sample-1 (Validamycin 60% w/w) @ 45, 60 and 75 ppm, sample-2 (Hexaconazole 2.5% w/w+Validamycin 8.5% w/w) @ 55, 82.5 and 110 ppm and sample-3 (Streptomycin 9% w/w+Tetracyclin hydrochloride 1% w/w) @ 50, 75 and 100 ppm were tested. The result showed that Antibiotics have inhibitory effects on T. harzianum. Unsatisfactory performances in terms of per cent growth inhibition (<80) were recorded on crop infecting fungi. C. theae treated with sample-1 @ 75 ppm and C. gloeosporioides with sample-2 @ 110 ppm had shown maximum 25.50 and 54.19 per cent growth inhibition, respectively. The highest 70.53 per cent growth inhibition of C. theae was observed in sample-3 treated @ 100 ppm. Considering the findings it can be recommended not to use above antibiotics with their respective concentrations in plant agriculture for controlling diseases caused by the said fungi.