Novel series 2-(2-imino-4-thio-5-substitutedbiureto-1-yl)-4-(3-substituted thiocarbamido-1-yl)-6-substitutedimino-1,3,5-thiadiazine [3a(i) to 3f(iii)] have been obtained by basification of their hydrochlorides [2a(i) to 2f(iii)] in presence of ammonium hydroxide solution, which are synthesized by the interaction of 1,3-bis-(N-substitutedamidinothi-ocarbamido)-thiocarbamide(1a-1f) and aryl/alkylisocyanodichlorides. The latter were prepared initially by the condensation of aryl/alkylisothiocyanate with 1,3- Diformamidinothiacarbamide. The structure of all these compounds was established on the basis of IR and PMR spectrum data. All the synthesized compounds have been assayed for their antibacterial activity against both gram-positive and gram-negative human pathogens.