In this study, 4'-(phenylurenyl/thiourenyl) chalcones (14-25) were prepared from 4'-(phenylurenyl/thiourenyl)acetophenones and benzaldehyde derivatives by Claisen-Schmidt condensation. In vitro inhibition effects of chalcone derivatives on purified carbonic anhydrase I and carbonic anhydrase II were investigated by using the CO2 hydration method of Maren. The result showed that all the synthesized compounds inhibited the CA isoenzymes activity. 18 and 19 were found to be most active (IC50 = 25.41 m M and 23.06 mu M) for hCA I, respectively. For hCA II, 24 is the most active compound (IC50 = 14.40 mu M).