Condensation of 3-acetyl-2,5-dichlorothiophene with 1- or 2-naphthaldehyde led to theformation of the new chalcones (3a,b) in high yields. The latter chalcones were used as a backbone for the synthesis of substituted 3-(2,5-dichlorothiophen-3-yl)-4,5-dihydro-5-(naphthalen-1 or2-yl)-1H-pyrazole (4a-h) in good yields. All newly synthesized compounds were characterized bystandard spectroscopic techniques. The microbiological activity of these new compounds wasinvestigated against bacteria and fungi. The new compounds showed good to excellent activityagainst all microbial species used for screening.