In search of new potential antimicrobial agents, series of trisubstituted 4.5-dihydropyrazoline derivatives have been synthesized starting from chalcones. A mixture of 4-phenylbut-3-en-2-one (1, 0.001mmol), phenyl hydrazine hydrochloride (2a-g 0.001mmol) and sodium acetate (0.002mmol) in ethyl alcohol was stirred at room temperature for 1 hr to get trisubstituted 4,5-dihydropyrazoles (3a-g) in good yield. Spectral, X-ray diffraction and elemental analysis confirmed the structures of the products. The synthesised compounds have been evaluated in vitro for their antimicrobial activity. The results revealed that some compounds particularly with chloro substituents act as potential antimicrobial agents
