Selective Mcl-1 inhibitors may overcome the drug resistance caused by current anti-apoptotic Bcl-2 protein inhibitors in tumors with Mcl-1 overexpression. Based on previously discovered compounds with a 3-phenylthiophene-2-sulfonamide core moiety, in this work, we have obtained new compounds with improved binding affinity and/or selectivity under the guidance of structure-based design. The most potent compounds achieved sub-micromolar binding affinities to Mcl-1 (<i>K</i><sub>i</sub> ∼ 0.4 μM) and good cytotoxicity (IC<sub>50</sub> < 10 μM) on several tumor cells. <sup>15</sup>N-heteronuclear single-quantum coherence NMR spectra suggested that these compounds bound to the BH3-binding groove on Mcl-1. Several cellular assays revealed that <b>FWJ-D4</b> as well as its precursor <b>FWJ-D5</b> effectively induced caspase-dependent apoptosis, and their target engagement at Mcl-1 was confirmed by co-immunoprecipitation experiments. Treatment with <b>FWJ-D5</b> at 50 mg/kg every 2 days on an RS4;11 xenograft mouse model for 22 days led to 75% reduction in tumor volume without body weight loss.