Carbonic anhydrases (CAs, E.C.220.127.116.11) play a critical role in many important physiological events and treatment of some diseases. Flavonoids or phenolic compounds have been discovered as novel CAs inhibitors instead of the traditional sulfonamides, with different binding to CAs, pro-drug activities, and new inhibition mechanisms. Here, we investigated the inhibition effects of some flavonoids including malvin, callistephin, oenin, pelargonin, silychristin, and 1-(4-methoxyphenyl)-2-methyl-3-nitro-1-H-indol-6-ol (ID-8) against hCA I and II, which purified from human erythrocytes by affinity column chromatography. Both hCA isoenzymes were inhibited by flavonoids, with IC50 and K-i values in the range of 2.34nM to 346.5M and 51.01-99.55M for hCA I and 86.60-750.00M for hCA II, respectively. These results showed that flavonoids especially malvin and oenin effectively inhibited hCA I and II isoenzymes. Hence, they may be used as an effective CA inhibitor in medical applications for treatment of certain diseases such as glaucoma, in the future.