Novel series 2-(1-substitutedguanidino-3-yl)-4-(3-phenylthiocarbamido -1-yl)-6- substitutedimino-1,3,5-thiadiazine [3a(i) to 3f(ii)] have been obtained by basification of their hydrochlorides [2a(i) to 2f(ii)] in presence of ammonium hydroxide solution, which are synthesized by the interaction of 1-Formamidino- (N-phenylthioamido)-5-phenyl-2-thio-4-iminobiuret (1a-f) and N-aryl/alkylisocyanodichlorides. The latter were prepared initially by the condensation of substitutedisothiocyanate with N phenylformamidinoformamidinothiocarbamide. The structure of all these compounds were established on the basis of elemental analysis, IR and PMR spectral data.