Herein, we report the synthesis, characterization, and carbonic anhydrase (CA) inhibition of the newly synthesized Schiff's bases 4-18 with benzenesulfonamide, methanesulfonamide, and methylsulfonylbenzene scaffolds. The compound inhibition profiles against human CA (hCA) isoforms I, II, IX, and XII were compared to those of the standard inhibitors, acetazolamide (AAZ) and SLC-0111 (a CA inhibitor in Phase II clinical trials for the treatment of hypoxic tumors). The hCA I was inhibited by compounds 4a-8a with inhibition constants (K) in the range 93.5-428.1 nM (AAZ and SLC-0111: K, 250.0 and 5080.0 nM, respectively). Compounds 4a-8a proved to be effective hCA II inhibitors, with K ranging from 18.2 to 133.3 nM (AAZ and SLC-0111: K, 12.0 and 960.0 nM, respectively). Compounds 4a-8a effectively inhibited hCA IX, with K in the range 8.5-24.9 nM; these values are superior or equivalent to that of AAZ and SLC-0111 (K, 25.0 and 45.0 nM, respectively). Compounds 4a-8a displayed effective hCA XII inhibitory activity with K values ranging from 8.6 to 43.2 nM (AAZ and SLC-0111: K, 5.7 and 4.5 nM, respectively). However, compounds 9b-13b and 14c-18c were found to be micromolar CA inhibitors. For molecular docking studies, compounds 5a, 6a, and 8a were selected.