Various pyrimidine derivatives (1a-c) were synthesized using the Biginelli three component cyclocondensation reactions of a beta-diketone, arylaldehyde, and thiourea, under microwave irradiation and conventional conditions. The acetylation of compound 1a gave 3-acetyl thioxopyrimidin 2. Also, thiazolopyrimidine (3) and (4) derivatives were obtained by a simple one-pot condensation reaction of starting compounds 1a, and 1b with 2-bromopropionic acid. The prepared compounds were screened for their antimicrobial activities against Gram-positive, Gram-negative bacteria and fungi using micro dilution procedure. The results of the study showed that the compound 4 was effective and selective for antimicrobial activity against the tested bacteria and fungi. Thus, we suggested that the compound 4 might be a new potential antimicrobial substance for bacteria and fungi.