Grey mold and white mold are significant vegetable diseases. They are caused by fungus called Botrytis cinerea and Sclerotinia sclerotiorum. A mentioned disease has large economic importance. Species are cosmopolitan polyphagous pathogens which in a big measure attack a large number of plant species. Besides attacking fruit species, they also attack vegetable species and agriculture crops. Ascomycete fungus Trichoderma longibrachiatum from genus Trichoderma, which are known as bio-factors in biological world, is mycoparasite of sclerotia of those pathogenic species, and mycelium also. This fungus is special antagonist contrary to pathogenic species, therefore objective of this research was to see into antagonistic activity isolate STP1 Trichoderma longibrachiatum on Botrytis cinerea and Sclerotinia sclerotiorum in laboratory “in vitro” terms of “dual cultures” method. Experiment was set up and conducted in Institute of phytopathology of University of Agriculture in Zagreb. In this experiment were used cultures aged 7 days and confrontation od STP1 with every pathogenic species was carried out. It was set up by random block schedule in five repetitions with four variants. Species T. longibrachiatum, faster and to a greater extent, took nutrient substrate by its rapid growth and development of micellar colonies from phytophatogenic species B. cinerea and S. sclerotiorum. Forth day after setting up the experiment it is apparent that isolate STP1 inhibited species S. sclerotiorum with Index of inhibition about 63 %, and B. cinerea with Index of inhibition 25 %. Further, in the seventh day percent of inhibition between two pathogen isolates differs which means that isolate STP1 whith Index of inhibition of 89 % inhibited to a greater extent than B. cinerea with Index od inhibition of 85 %. The results confirmed hypothesis of antagonism between those three species, that is that species T. longibrachiatum demonstratet antagonism towards B. cinerea and S. sclerotiorum. Antagonism was based on mehanism of competition beacuse species T. longibrachiatum STP1 was faster colonized nutrient substrate from the other two pathogen species privative them space to growth and nutrients from nutrient supstrate. Also, in experiment with S. sclerotiorum mycoparasytizm was confirmed considering that STP1 parasitited mycelium and sclerotia of this pathogen. However, in control and test dishes there were no developed sclerotia by other pathogen B. cinerea.