Some new 3-(5,6-Diphenyl-1,2,4-triazin-3-yl)-5-substituted- 1,2,4-triazino[5,6-b]indole derivatives (6-12) have been obtained via treatment of both (4 and 5) with p-nitro-benzoyl chloride, ammonium thiocyante, formaldehyde-methanol, acrylonitrile and thiosemi-carbazide. The former structure of the new products was established by the help of elemental analyses, as well as spectral data. Some of their showed pronounced effect on the Cellobiase produced by Thermomyces lanuginosus and Chaetomium thermophilum.