A new series of 1,4-dihydropyrimidinone (DHPM) substituted diaryl urea and thiourea derivatives were synthesized and their inhibitory effects on the activity of purified human carbonic anhydrase (hCA) I and II were evaluated. 4-Nitrophenyl-1,4-DHPM was prepared with dimedone, nitrobenzaldehyde and urea or thiourea and nitro group was reduced to amine derivative. The compound was reacted with isocyanates and isothiocyanates to get the final products. The results showed that all the synthesized compounds inhibited the carbonic anhydrase isoenzyme activity; 4c (IC50 = 66.23 mu M for hCA I) and 4f (IC50 = 63.09 mu M for hCA II) have the most inhibitory effect. The synthesized compounds are very bulky to be able to bind near the zinc ion and they much more probably bind as the coumarins and activators.