To synthesize a variety of Pyrimidine linked with 1,3,4 thiadiazole mannich bases and their Biological activity was determined. Using 3-phenylpropiolaldehyde and Acetamidine hydro chloride, new compounds were synthesized .The structure of all the new compounds are established on the basis of FT-IR, 1H NMR, 13C NMR and Mass spectral data. For antibacterial studies were done by Staphylococcus aureus ATCC 9144, Bacillus Cereus ATCC 11778, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 2853. For antifungal, Aspergillus Niger ATCC 9029 and Aspergillus fumigatus ATCC 46645 model. All the compounds were synthesized in good yield. Among the new compounds 8a,8b are found to most biological activity. The results obtained justify the usage of these compounds from their antifungal and anti bacterial activity. Therefore the nature of groups is very important for antifungal and antibacterial activity.