Here, we formulated and investigated the structure-activity relationships of novel N-substituted carbazole sulfonamide derivatives with improved physicochemical properties. Most of these new compounds displayed good aqueous solubility. Certain molecules presented strong in vitro antiproliferative and in vivo antitumor activity. Relative to the control, 50 mg/kg compound 3v substantially reduced human HepG2 xenograft mouse tumor growth by 54.5% and its efficacy was comparable to that of CA-4P. Compound 3h demonstrated anticancer efficacy in both subcutaneous and orthotopic HepG2 xenograft mouse models. We also developed a novel synthetic method for 7-hydroxy-substituted carbazole sulfonamides. Compared with the control, 25 mg/kg compound 4c inhibited human HepG2 xenograft mouse tumor growth by 71.7% and was more potent than 50 mg/kg CA-4P with only 50% tumor shrinkage efficacy. Among the three water-soluble carbazole sulfonamide derivatives formulated in the present study, compound 4c displayed the most effective tumor growth inhibition in vivo and merit further investigation as potential antitumor agents for cancer therapy.