Fused pyrimidines play an imperative role in our life due to their biological importance in the struggle of microorganisms. A series of 4-aryl-3-methyl-1-phenyl-1,4,6,7-tetrahydropyrazolo[3,4-d] thiazolo[3,2-a]pyrimidine (4a-j) were synthesized by cyclization of 3-methyl-1-phenyl-4-aryl-1,4,5,7-tetrahydro-6H-pyrazolo[3,4-d]pyrimidine-6-thiones (3a-j) with 1,2-dibromoethane in presence of anhydrous potassium carbonate. Earlier, compounds (3a-j) were synthesized by the condensation of 5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one (2), different substituted benzaldehyde and thiourea with catalytic amount of con. HCl in methanol. Compound 2 was synthesized by condensation of ethyl acetoacetate (1) and phenylhydrezine in presence of a catalytic amount of acetic acid at reflux temperature. The constitution of the synthesized products has been characterized by using elemental analysis, Infrared, ¹H-NMR spectroscopy and further supported by Mass spectroscopy. All the products have been screened for their in-vitro biological assay like antibacterial and antifungal activity at concentration of 500 μg/ml. It was exposed that most of the compounds displayed inspiring antibacterial and antifungal activity compared to the used reference standard.