C188 is a cell-permeable naphthol compound and a STAT3 inhibitor. C188 inhibits IL-6-stimulated STAT3 Tyr705 phosphorylation and nuclear translocation in HepG2 cells by targeting STAT3 SH2 domain peptide-binding pocket, while exhibiting little effect against IFN-gamma-stimulated HepG2 cellular STAT1 phosphorylation.