The effects of some phenolic sulfonamides were determined on the cytosolic carbonic anhydrase isoenzyme I and II (hCA I and II). Both isoenzymes were purified separately from human erythrocytes, using the Sepharose-4B-l-tyrosine-sulfanilamide affinity column chromatography method. In continuation of the study, we identified the inhibitory effects of phenolic sulfonamides 1–4 on the esterase activity of hCA I, and II. The inhibitory effects of phenolic sulfonamides 1–4 were tested on human carbonic anhydrase isoenzymes hCA I, and II. Among the compounds 1–4, compound 1 was concluded to show the best inhibitory effects. According to our data, IC50 values of compound 1 were found as 3.55 and 2.94 μM for hCA I, and hCA II, respectively. On the other hand, Ki values of this compound were found as 0.827 and 0.745 μM for both isoenzymes, respectively