Novel 1,3,5-triaryl-4,5-dihydro-1H-pyrazole derivatives like 5-(2,4-Dichlorophenyl)-3-(3-fluoro-4-methoxyphenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (3a-p) were synthesized from 3-fluoro-4-methoxy acetophenone and screened for their antibacterial activity. Chalcones (2a-f) prepared by condensation of 3-fluoro-4-methoxy acetophenone with different aromatic aldehydes were reacted with phenyl hydrazine hydrate or substituted phenyl hydrazine to obtain 1,3,5-triaryl-4,5-dihydro-1H-pyrazole (3a-p). Structures of the synthesized 1,3,5-triary-4,5-dihydro-1H-pyrazole compounds (3a-p) were characterized using IR, 1H NMR, 13C NMR, MS spectral data. All synthesized compounds screened for their antibacterial activity against E. Coli, P. aeruginosa, S. aureus, B. Subtilis with standard drugs ampicillin and ciprofloxacin. Some of the 1,3,5-triaryl-4,5-dihydro-1H-pyrazole derivatives, specially 3f, 3m, 3n and 3p showed excellent antibacterial activity and have the potential to convert into antibacterial agent.