Endolichenic fungi are considered a promising source of new materials. For further evaluation of some biological activities of the Trichoderma strains isolated from lichens Dirinaria spp. and Cryptothecia spp., their antifungal and antibacterial activities were screened by the methods of dual culture and environmental toxicity. Substrate degradation was evaluated using the qualitative enzyme assays. Fourteen strains of Trichoderma spp. were isolated from 60 lichen samples. All the isolates were able to inhibit the radial growth of tested fungal strains (Bipolaris spp., Colletotrichum spp., Corynespora cassiicola, and Fusarium spp.). Otherwise, only 12/14 isolates were found capable of competing for substrates with Ralstonia solanacearum. The cell-free supernatant obtained from the cultures possessed both antifungal and antibacterial activities. The antagonistic activity of the isolates was selective. Most of the isolates were able to degrade at least one of the investigated substrates, namely cellulose, pectin, and starch. All strains could produce peroxidase; none of the isolates possessed laccase and tyrosinase. A potential antagonistic fungal strain VDT6 has been identified as Trichoderma harzianum. The assessment results indicated that the Trichoderma isolates could be used in agriculture as biological control agents.