This book is very useful for the researcher and academia who are working on Pyrimidine derivatives. This book deals with spectroscopic characterization of synthesized pyrimidines. This books contain one separate chapter for antimicrobal activity. All synthesized compounds were tested for their microbial screening. The synthesis of chalcones was carried out by one pot condensation of 1-chloro-(4-tolyloxy) benzene with 1-(4-hydroxylphenyl) ethanone followed by condensation with various aromatic aldehydes. Prepared chalcones were refluxing with guanidine to yields various pyrimidine derivatives. All the prepared compounds were characterized in by 1H NMR, 13C NMR, IR, MASS spectroscopic techniques. Biological evaluation of mention compounds was also made in terms of gram positive bacteria such as Staphylococcus aureus, Bacillus megaterium and gram negative bacteria Escherichia coli, Proteus vulgaris.