A new seriesof 4-aryl-5-cyano thiouracilderivatives 4(a-c)was synthesized by reacting ethyl cyanoacetate, thiourea or substituted thiourea and aromatic aldehyde in presence of anhydrous potassium carbonate. The main target compound 4-(p-chlorophyll) -2- mercapto -6 -oxo-1,6- dihydropyrimidine-5- carbonitriles ( 4a) were reacted with chloroacetyl chloride , chloroacetonitrile or oxalyl chloride to give 2,5-dioxothiazolopyrimidines, 3-amino-5- oxothiazolopyrimidines and 2,3,5-trioxothiazolopyrimidines 5,6,7 respectively . Derivatives of 2-substituted benzylidne 3, 5-dioxothiazolopyrimidines 8a, b were prepared via reacting 4a with chloroacetic acid, aromatic aldehyde and anhydrous sodium acetate in presence of a mixture of acetic acid and acetic anhydride. Reacting compound 9 which was obtained by refluxing compound 4a with hydrazine hydrate , with formic acid or acetic anhydride give the respective triazolopyrimidines 10,11 .On the other handthe pyrimidotriazines 12,13 were obtained by the action of compound 9 with diethyl oxalate and ethyl bromoacetate in sodium ethoxide respectively. Reacting compound 9 with different aromatic aldehyde in glacial acetic acid gave a series of azomethene compounds 14(a-d). All the newly formed compounds are evaluated for their antimicrobial activity .It was found that some of the tested compoundshas variable activity against the selected strain.